Honestly, forget the Dells.
Check out a site like ibuypower.com, cyberpowerpc.com, or monarch.com and put together a decent AMD socket 939 system. you get more options and choices (like different cases, motherboards, brands of RAM, brands of hard drives, graphics cards {real ones, not crippled ones like Dell uses}, and so forth).
Or you can build, which is not as hard as you think. Plus you can get plenty of help here in threads and tutorials (including two or three with step by step pics). Everyone here is more than willing to help.
If you are determined to go with a pre-built, check this one out:
http://www.tigerdirect.com/applicati...CODE=WEM1184IS
It's a single core, but it is a decent system for a starter. Just add a graphics card and a beefier PSU and you're ready to rock and roll.