I have a Dell which is over 2 years old now but fabulous.
What i would recommend is:
2 GB RAM
Dual Core processor or really a Quad if at all possible. They have different processing speeds in amongst that so probably min 6550 but 6600+ if you can stretch that far.
Get a dedicated graphics card - 256 min but 512 if at all possisble
AND compare battery life! Battery life differs hugely. Mine lasts about 4-6 hours but I have a friend with a Toshiba that last maybe an hour.
This is Aussie Dell but it gives you a good guide on what to look for based on the performance you want
http://www1.ap.dell.com/content/prod...hs1&l=en&s=dhs