My first build, need a little help!

The link for the mobo is tough to find the mobo your talking about. It should be like this link:
GIGABYTE GA-EP45-UD3P LGA 775 Intel P45 ATX Intel Motherboard - Retail

PSU should work with the case. I'd recommend saving some $ and get the CM690 case instead for $84 shipped!! It has plenty of room for 99% of builds and comes well equipped!
Cooler Master 690 without Power Supply
Newegg's link to the CM690, which has more details than the Buy.com site does.

What are your other parts and what is your budget for the build??

i was going to order
vista home premium,
4 GB ram,
a decent size but fast hard drive,
and a good ati video card
with the core 2 duo 3.0ghz

my budget is about $600, but it looks like i might go over

is the mobo good though?

Okay the mobo should be just fine. I'd consider getting the e5200 for $83 shipped (2.5 gHz) and OC it to 3-3.8 gHz, depending on which cooler you use. 3-3.2 gHz should be fine on stock cooling and for under $30 you can add the Arctic Cooling Freezer Pro 7 CPU HSF. It's up to you, but the cheapest way is to get the easily OC'd e5200 and use the extra $ for a good GPU/Case/PSU. Which you have already listed the 750tx, which is a good buy. Depending on budget and configuration you can even go with the Antec 500w Earthwatts PSU for $50 and save some $ for whatever you need.
Recap:
CPU - $83 e5200, OC's to almost 4 gHz!!
Mobo - $120 - $20 MIR Gigabyte p45 mobo you listed
RAM - $50 4gb's DDR2 800 mHz is all that you really need. Runs at stock 1.8 or 1.9v!!
HD - $70 WD 640 gb's HD AAKS version
Case - $54 Antec 300 (saving $ here to allow other parts to be bought)
PSU - $50 Antec 500w Earthwatts PSU, 34A on the combined 12v rails, >80% efficient!
GPU - $170 - $20 MIR = $150! 4850 512mb version would be a good selection.
OS - $80 Home Premium 64 bit
DVD Burner - ~$30 Just remember to get a RETAIL version, so you get the software to read/burn DVD's!

Total ~$700 - $40 MIR's = ~$660!! Over budget, but not sure if this works for you or not. Could adjust the GPU some, depending on what you want to do. I probably wouldn't go below a 4670, 4830, 9600gso/gt, 9800gt, if you going to be any higher end games. It's going to depend on what your resolution that you'd be playing at and what games your going to be running.

Tom's Hardware build of e5200 OC'd to about 4 gHz w/4850 GPU

Also look for deals tomorrow on Cyber Monday, because you might be able to save some good $on some of the parts you need! You'll need to jump on them if you find some of the parts tomorrow though.

dude, you're awesome! thanks

gonna wait to see if there are any deals tomorrow