I want to build my own computer but I need advice for a lot of things. I want to spend the least amount of money possible. I will be using it for everday use and some gaming (WoW/Bf2). I have a radeon x300 se that I can use for a little while. I dont plan on using SLI anytime soon.
Here are some of the parts i'm thinking about using.
 
-AMD Athlon 64X2 Brisbane 2.5ghz cpu
http://www.newegg.com/Product/Prod [...] 6819103212
-WD 160 gb hdd
http://www.newegg.com/Product/Prod [...] 6822136075
-Case? - Zion mid tower case w/ 450 psu
http://www.newegg.com/Product/Prod [...] 6811208005
Someone was telling me that 450w psu would be pushing it but I dont think so.
-I plan on buying 2gb ddr2 800 ram  
Im not sure what to get as far as an OS and mother board. Ive been looking at the 690g motherboards but I dont really know what's good or bad.  
Will I be needing extra cooling for the cpu even if I dont plan on overclocking (paste/extra fans)?
If im going to be connecting to the internet through a wireless router, what will I need?
 

Max budget?

Im trying to get it together for under 300$ (CPU, Motherboard, Hdd, Case w/ psu, Ram, optical drive?)

Someone was giving you good advice.  That PSU may have a 450W rating but it only supplies 216watts to the important +12v rail.  

Thats less than some 380watt PSUs
http://www.newegg.com/Product/Prod [...] 6817371005 Antec Earthwatts 380w PSU = 27amps of +12v power.
 
The stock AMD heatsink/fan will work fine for CPU cooling in a non-overclocked system.

Well i just assumed that it would be enough because our family desktop is running more on a 305w dell psu.  
 
Would it be better if I bought the psu and case serperately?

You'll need a "wireless adapter".  You can get them in internal or external (via USB) models.
http://www.newegg.com/Product/Prod [...] 6833127080DLink 802.11b/g Internal PCI card

 
http://www.newegg.com/Product/Prod [...] 6833156152Trendnet 802.11b/g External USB adapter

Any suggestions on internal vs external?

Whatever is cheaper.  I'm using an external usb adapter, and it works great.
 
For the rest of it, start here:
Tom's Hardware $500 Gaming PC
 
You can remove the graphics card, saving $130.  You can also remove the Cooler Master HSF, saving $25.
 
That drops your price to $345.  Now remove the processor and motherboard.  You are now at $187, giving you $113 for motherboard / processor.
 
Now, to look for deals.  You can get a HDD and processor for $98.  Newegg has a combo deal going on.  Look at the bottom of this page, a 2.2ghz brisbane and 160GB wd.
 
Doing that makes your build the following:
Case: Antec NSK4480B - $66 (according to Tom's)
PSU: Included
Graphics: Already own
HDD: WD 160GB - $98
CPU: 2.2 GHZ Brisbane - Included with HDD
RAM: G-Skill/Wintec/A-Data 2x1gb DDR2 (667 or 800) - $42
Optical: DVD/RW: Philips / Samsung / Lite-On - $25
 
Leaving you at $231.  A wireless adapter costs $18 - 80 or more, I'll assume $25.
 
That puts you to $256.  Leaving $44 for a motherboard.
This Abit motherboard is AM2 / AM2+, leaving room for more processor upgrades in the future.   It runs $53, with a $10 MIR.  That puts you just below your $300 threshold.
 
Hopefully someone out there will be able to give you some more info on if that is a good chipset (I know Intel mostly), but it is a machine in your budget.  You'll have to move quickly on some of it, and shop around for the best price but it's an idea.

That Dell 305W PSU has 22amps of +12v power.  450W PSU in that Xion case has 18amps.
That Antec NSK4480B case litlrabi suggested has that Antec Earthwatts 380 PSU with 27amps +12v.  
 
Internal vs external wireless adapter.  The only real disadvantages to the USB type are (1) its a little too easy for someone walking by to remove it and (2) it takes up a USB slot (and sometimes 2 USB slots depending on how your case has its USB slots arranged.  The internal PCI card with external antenna usually has the edge in getting a better signal if you're farther away from the wireless hub.  
 
 

Are there some disadvantages to using a micro atx case? Less room and ports? Space isnt an issue for me.
Ill list some cases and see what you guys think. Im just trying to get a good of what will work.
http://www.newegg.com/Product/Prod [...] 6811226022 (no reviews yet)
http://www.newegg.com/Product/Prod [...] 6811146041
http://www.newegg.com/Product/Prod [...] 6811146025
 
So in a psu, high wattage doesnt mean anything with low amps? Do I have to worry about the "rails"?
http://www.newegg.com/Product/Prod [...] 6817170010 good?
Im still not really sure how to determine a good psu from bad one.
 
Im willing to spend on a little more so that I can get a good motherboard and processor. Heres a couple of cheap motherboards ive been looking at.
http://www.newegg.com/Product/Prod [...] 6813128056
http://www.newegg.com/Product/Prod [...] 6813128043
 
 

Either of those motherboards are a good bet.
Be sure you know the differences between 690V (Ati 1200 video chip) and 690G (Ati 1250 video chip)
Also be sure the motherboard has the right ports for other peripherals  (parallel printer port vs USB printer, etc)  
You can also compare MBs side by side for feature/price comparison:
http://www.newegg.com/Product/Prod [...] 22&bop=And
 
MicroATX is a bit less easy to work inside the case - not really factor if you're not working on the PC on a regular basis.  It does have less expansion slots (PCI-e & PCI) through the back of the case - but there is one opening for each of the slots on a MicroATX MB like the 690V/G.  
MicroATX vs MidATX cases.
http://www.newegg.com/Product/Prod [...] =3&bop=And
 
It's less about total wattage then how the wattage is distributed.  Modern systems need more +12v and less +5v than systems in the past.  Dual +12v rails is a nice feature but not anymore important than a single +12v rail with more amperage - in the 22-25amp range for example.  
I noticed you were looking at $50 cases and $25 PSUs.  IMO that should be $50 PSUs and $25 cases (or maybe $40Psu and $35 case.    
You can find bargins and still get decent options.  On your budget and with the hardware you want to put inside the case I think this is one of those decent options.
http://www.newegg.com/Product/Prod [...] 6811190086
 

OK thanks a lot. I was looking around and found this motherboard. I want something that I can still if I need to change something.
http://www.newegg.com/Product/Prod [...] 6813138106
 
When buying a psu are looking for more amps in the 12v rails? Is 20+4 pin the same as 24 pin?
http://www.newegg.com/Product/Prod [...] 6817339012