If you want something premade, then as Coastie said, it's good to find a cheap computer with a good processor, then upgrade from there. For instance, here is an amazing deal for a Gateway that comes with a Q6600, as well as plenty of other goodies:
Gateway GT5678: $779.99
Intel Q6600
4GB DDR2 667
750GB SATA2
18x DVD Burner
HD2400XT 256MB
Included keyboard, mouse, and speakers
Windows Vista Home Premium
The only problems are that it doesn't come with a monitor, and the video card is crap, but they are both easily fixed. Along with the new video card, should be a new power supply. This is because the included power supply with the computer either wouldn't have the power necessary to run a modern video card, or wouldn't have the cables necessary to power it. Unfortunately though, you might want to get your friend to help you on the power supply installation, since I'm not sure if you know where everything plugs in and such.
EVGA 8800GTS: $229.99
Acer 19" LCD: $179.99
Corsair 650W PSU: $109.99
Total price: $1299.96 (excluding shipping and rebates)
So that's a cheaper alternative if you sub out a few parts. With the Q6600, you'll be future proof for when apps and games start to utilize multithreading. The 8800GTS is still one of the best cards out there for the price, and will play modern games for years to come. 4GB of RAM is plenty for gaming, and a good amount for Vista. The 650W PSU leaves some headroom if you ever want to add more components. Lastly, 750GB is a good chunk of storage, but there's always room for more hard drives if you need it.
If you do ever want to make a custom built computer, then don't hesitate to ask. I think it's better, since you have a lot of quality parts to choose from, and you can customize everything down to the last detail as you see fit. Plus, it's a great experience, and lots of fun. But it's entirely up to you.
Athlon X2 5000 BE 3.1GHz, Arctic Cooling Freezer 64 Pro, Gigabyte GA-MA770-DS3 AM2+, Visiontek HD4850, Corsair XMS2 2GB DDR2 800, OCZ StealthXStream 600W PSU