Well, you can't especially compare AMD's and Intel's anymore when it comes to gaming, but you can just look at the ratings. Like an Athlon 64 3400 is comparible to a P4 3.4GHz. That's not exact, but it's the best way to look at it.
Now onto the specs...
CPU: I'd recommend an AMD for sure, somewhere around an Athlon 64 3500.
http://www.newegg.com/app/ViewProduc...103-463&depa=1
Hard Drive: I'd go with around a 120GB 7200RPM, probably a Seagate would be your best bet.
http://www.newegg.com/app/ViewProduc...148-022&depa=1
Motherboard: I'd go with a higher end board, like an MSI K8N Neo2 Platinum
http://www.newegg.com/app/ViewProduc...130-468&depa=1
And even though you didn't ask for it:
Video Card: GeForce 6800GT, no doubt
http://www.newegg.com/app/ViewProduc...130-203&depa=1
PSU: a 480W will do you good, and this is a great one.
http://www.newegg.com/app/ViewProduc...153-007&depa=1
RAM: I'd go with 1GB of some good RAM, and I've heard some good things about this stuff.
http://www.newegg.com/app/ViewProduc...220-033&depa=1
Sound Card: Onboard sound would do you OK, but if you want a good sound card, look no further than this one.
http://www.newegg.com/app/ViewProduc...102-179&depa=1
Speakers: Depending on what you really want to spend, here's a good set of 5.1CH speakers. If you want something better, there are better choices, but these would be one of my top choices:
http://www.newegg.com/app/ViewProduc...121-121&depa=1
A couple of those items from NewEgg are out of stock because of the holidays, but check back there later or go to
http://www.pricewatch.com and check around there for a good price.
Hope that helps ya out!