HP installs alot of "boatware" that is really unneccessary, (i.e., that little "search" near clock, the yahoo/google BHO search bars at top near the address bar) as it performs the same function as Vista. Not to mention NIS- which is a major resource hog.
You want 2-4GB of ram. If you are running 2GB or less along with all the OEM bloatware then your comp will be sluggish. Make sure you have SP1 with all the updates, and try a full defrag of Windows.
start>in search type cmd, right click program and click "RUN AS ADMINISTRATOR"> in command prompt type defrag c: -w> click enter
(note- do not close command prompt screen until it is finished)