Good deal, I am seriously considering purchasing that machine. I would recommend a downgrade of the RAM from 4gb down to 3gb (Windows 32bit can only use a maximum of 3.3 gb). And I noticed that you're "upgrading" from the original 3gb that runs at 800Mhz, the 3gb at 800Mhz is more suitable for gaming. Also, keep in mind though, that there have been numerous Dell threads that talk about how the eSATA port doesn't work. It's fixable, but the current solution is a complete clean reinstall of Vista. If that's not a huge problem for you, then this deal definitely looks really sweet.
I'm just looking to upgrade from my old computer to something a little more modern. I mostly use the the computer to browse the internet and play games. I'm not looking to spend too much on a new PC but this is the best deal i have found:
DELL XPS 420