You don't seem like one to worry about a budget, but its always best to keep in mind a final total dollar amount.
Certainly u want a motherboard that combines PCI Express bus instead of the old AGP bus; PCI ex or PCI x adds a great start for video editing.
As for hard drives, you should have 2, that way u can make ur C drive more efficient by sending the Swap file, and the Temp internet folder to the separate 2nd drive. You should also make a Folder called ProgramFiles2 on the 2nd hard drive and Install your miscellaneous software on that 2nd drive. You'll be surprised that your pc wont slow down within a few years like most others do.
If you're going to be adding the new OS, Windows Vista, with your new hardware, you may be surprised or not, that there may not be a Vista compatible driver available for your new hardware as of yet. In this case, goto the manufacturers' website of the hardware in question and search for a Vista compatible driver.
Building your own pc, a few things to know after u get all ur parts.
Don't build your pc after you have walked around on carpet, unless u ground urself 1st. The static electricity build up in your body could damage your memory chips or motherboard during your build. You can ground yourself of static electricity by touching the back of a running computer's bare metal case and hold your fingers there from both hands on the bare metal for 10 seconds. Careful!, don't place your fingers in the fan or USB area.
Treat the hard drives with extreme care: a 1/8" drop on a hard surface of an hdd will cause irreparable sector damage inside, which could lead to Blue screens in the future or total unexplained loss.
THe inside of ur case may or may not have a manual and your motherboard should have a manual.
You should read all manuals very carefully.
One thing to watch out for is a polarity issue.
More specifically, the HDD light, and Power light terminals on the motherboard have extremely small lettering or abbreviations, usually in white.
What you are looking for in the white lettering is positive and negative.
a positive is usually a "+" plus sign. a negative is usually a dash.
Sometimes motherboard manuf's take a short cut to save space and only place a plus sign on the white lettering around the terminals.
There will also be power switch and reset switch terminals.
Its very important to get all the terminals perfectly oriented the 1st time u power on the motherboard! So read the manuals diagrams very carefully.
Some builders will say that there's no danger probably because they didn't take an electronics course, but only the engineer who built the board can tell you if there's a protection circuit built in to protect from blunders.
It always best to get it right the first time so you don't end up damaging your motherboard or power supply.
So inside your case, you will see very small colored wires with small black sockets on the ends.
It's important to know about whats common or ground and whats positive, this is called polarity of the wires in the case.
Your job is to match the polarity of the wires with the polarity on the motherboard.
A red wire is always positive, and black is always negative or common.
What if u have green and white wires? well usually green is common or negative, but it can also be positive and that all depends on your case wires. If you have no red or black wires and lots of green wires, for example :
green - white
orange - white
violet - white
for this situation, these 3 pairs, this means that white is common or ur negative ground because it appears most often.
the other colors will be the positive.
A word about installing your motherboard: your motherboard will come with a rear face plate. Lay the case on your bed, or desk and open both sides of the case, usually 4 screws on the back, use a #2 screwdriver. Within the case you will see a large opening, this opening is where the motherboard will be going into. First you press in the face plate to the back of the case...watch your fingers!! sometimes the edges are extremely sharp inside a case! Make sure that the rear face plate is fully pressed in and all sides are equal. Take your motherboard out of the box and un wrap it. You must try to not touch any metal part on the motherboard!
Assuming you got a standard bag of scres with your case, you then look for brass stand offs. Count the number of holes in your motherboard, usually 3 or 4 in the rear and 3 or 4 in the middle. Usually the holes are not symmetrical.
Examine your motherboard carefully to determine which holes in the case get the brass stand offs.
Also test one of the small chromed screws into one of the brass stand offs for looseness, usually you use the coarse threaded screws to go into the standoffs. Then screw in the stand offs untill they are very finger tight.
Gently place you new motherboard on top of the standoffs within the case, and assuming all holes are matched, start ur screws without dropping any.
Most standard case bags of screws, you'll get 2 types of screws, fine thread and coarse thread. The fine thread screws are usually used on drives. The coarse threaded ones are usually used on the motherboard, expansion cards, some hard drives, internal and external case areas, and the power supply. Now! if u get little red gaskets with your bag of screws then usually these are used to go under the screws to protect the motherboard from too much tightening pressure.
So screw, gasket, motherboard, standoff.....if u dont see gaskets then don't worry about it, just be very careful not to tighten the motherboard screws too much....IF YOU HEAR CRACKING or CRACKLING while tightening the screws...STOP immediately!! you may have tightened too much and possibly caused a crack in your motherboard. If your motherboard doesn't bootup then that could be the problem.
Never over-tighten a screw, what u want to turn a screw to is about 5 pounds of pressure, and that's not much. The approximate tightness is about the same amount of force as closing a new water faucet.
Ok let's take a breather from assembly....let's suppose u connected everything right and then your screeen turns black upon booting...well that could be a number of things.
If your power supply fan is going, then it's not the power supply, Try reseating the video card or reseating the memory.
You see, putting your own pc together, you have to become your own technician
Ok some other points to consider:
Assuming you have a floppy drive as drive a or b:
Create a REstore point after everything is working and installed, and then Create a password Reset disk in case you get a nasty rootkit that changes the way you login. ( this is a necessity now for XP with SP2)
That pw reset disk can only be used for the pc it was made for. It can't be used on any other pc.
Microsoft has all the details about making a Password Reset Disk and how to use it. You should print out a copy of those instructions in case of a future emergency.
Your motherboard may have come with a Drivers cd. What this is is a cd with chipset, video, sound, LAN and USB drivers.
In general, this is the order of driver install after u have installed your operating system: chipset, then video, then LAN and USB, then sound. EAch one usually requires a reboot, so prepare to spend some time getting that right.
One last piece of good advice: don't buy into Vista right away, unless your really sure that all your hardware has all Vista Compatible drivers.
Wanna keep out the nasties, get 2 antivirus, 2 firewalls, and 2 anti-malwares.