I would WAY go for the HP. I worked for a major electronics chain for a while, during which I sold laptops/desktops. Acers....are cheap for a reason. They're a decent machine if you aren't going to ask too much from it (although, the hinges tend to go a bit quickly on them), but HP/Toshiba/Gateway, hell, even Compaq are way better in quality.
If you can afford the HP, go for it. If not (and not many can in this economy), then grab the Acer.
Intel Core 2 Quad Q6600 @ 3.2GHz
4GB Mushkin DDR2 1000
Kingwin Mach 1 1000 watt Power Supply
Asus 4870 x2 graphics card
Gigabyte GA-EP45-UD3P motherboard
Cooler Master HAF 932 case
Samsung SyncMaster T240
3DMark Vantage:
X7241 (all settings maxed)
CPU: 11207/GPU: 7109