the biggest thing with hp computers is the extra software installed on them. I sell hp, compaq, sony, gateway ( and emachines) and i know a little about the inner workings of the HP prebuilts.
First of all they come with alot extras you dont really need, software wise which is hard to wipe out of your system, also the support for HP's is really bad, hard to understand and even harder to get warranty service. If you do run into problems most computer repairmen(shops) will run away from you when you tell them its an hp.
To be honest with you, and this is going to catch alot of flack from everyone else, I would purchase the emachines athlon 64bit system, they are IMMENSELY easier to work on, they are now owned by gateway and they are more properly priced. If you must go for a prebuilt system, go with the emachines T6524:
brand name eMachines
manufacturer eMachines
model name T6524
processor type AMD Athlon 64 3500+
processor speed 2.2 GHz
frontside bus 2000 MHz
memory 1.0 GB
maximum memory upgrade 4 GB
memory speed PC3200
memory type DDR SDRAM
hard drive capacity 200 GB
video memory 128MB shared
video hardware ATI Radeon Xpress 200
audio hardware AC '97 6-channel audio
modem standard 56K V.92
Wi-Fi capability included (Wi-Fi ready) no
Ethernet port yes
infrared port no
included integrated drives DVD+R DL/DVD