If i were you i would hold out as long as possible at least hold out till january if you can, A newer Core2Duo will be out and even maybe a Newer Graphix card! I googled it and a website said that the 8800 will come out some time in NOV....
You are in luck i read that the 8800 GT will be like $440 but if i were you i would also invest in either a seperate PSU for it or a bigger power suply for your PC. It is going to be VERY power demanding.
1. What are you going to mainly using it for?
Gaming go for the Dell
Anything but High end gaming go for HP.
The HP can still game, but the E1705 is more upgradable. (Cpu,Gpu)(Core Duo to Core2Duo, 7800 to 7900GTX(with mod))