Thinking of building a pc....

[xXInsaneDylanXx]

Okay well first off I have a hd wide screen monitor and a cheap Emachine with a Intel Celeron and I put in a Geforce 8800 graphic card so I can watch moves and such through my tv via s-video. I don't have an HD tv so thats the best I can use. As you might have relised, Emachines aren't the greatest so I want something alittle better...besides Ive had this one for over 2 years too.
What I use my pc for is mostly common stuff. But what I want it to do smoothly is play movies(not HD though) and games. Like Crysis and such. I won't be hard core gaming on it since I have a ps3.
I don't know alot about all of this but as much as I know this seems to be a good set up:
Case- http://www.tigerdirect.com/applicati...&sku=C283-2032
Motherboard- http://www.tigerdirect.com/applicati...&sku=G452-0010
cpu fan- http://www.tigerdirect.com/applicati...9&sku=Z20-1018
total 4 gigs of ram- http://www.tigerdirect.com/applicati...3&sku=K25-4026
power supply- http://www.tigerdirect.com/applicati...&sku=C283-2036
processor- http://www.tigerdirect.com/applicati...=CP1-DUO-E8400
extra fans- http://www.tigerdirect.com/applicati...&sku=C283-1148
Graphics card- will be using my one right now but will get one sometime...NOT Geforce! The 8000s do not support full screen output to tv(not sure about 9000s)
sound card- built in one is good enough for me...for now

This will add up to be around 550bucks-I don't need a hdd, monitor, graphics card,(for now) dvd drive or OS. I can take that out of my existing pc.
I will be running 32bit custom modified xp for speed and stuff I like.

I know this isn't my final decision but I just want to hear from ppl who know more then me and what you think and what I should change...
I want something that I can upgrade for awhile, and as much as I know, this motherboard is a good one for that.(heard good things about this brand)
Also about bios, Im new to this and im not sure how to set up everything...so if you know a great site to learn about alot of this stuff would be great.
Or do you think I would be better off just buying a pre built one?
I know Im asking alot at one time but all help will be appreciated!
Edit: I can get most of this on newegg cheaper.