I've also a Dell E1505.
I have the previews version, with the Core Duo CPU.
The ATi Mobility Radeon X1400 will satisfy you if you play games occasionally. It can easily runs games like BattleField 2 and Need for Speed. I score arround 950 points in 3DMark06 ( Core Duo 1.66 Ghz, 512 MB DDR2 533 MHz, 80 GB @ 5400 RPM ).
Sure, a big gamer would like a GeForce Go 7600 or an X1800/Go7900, but you'll find this GPU's only in 17" laptops, which are heavier and less easy to carry. You lose the mobility of a laptop ...
Make sure to format your hard-drive after you receive your new computer. Manufacturers install ( too ) many useless software that slow down the computer ( you should see the msconfig startup tab ... ). You'll get better performances with a clean Windows XP.
I concil you to take the ATi. You'll get better Aero Performances in Windows Vista and better performances in video/photo editing tasks or 3D programs.