extremely slow system that should be very fast?

Hi!

I was wondering if you guys could help me on this one.
i have an HP pavilion zx5000, which i bought about 22 months ago.
Its a 2.8 Ghz Pentium 4 (not M), 2 Gigs of Ram, 128 Mb Ati Mobility Radeon 9600, and either the 4000 -something RPM 60 gig HD ( i think i ordered the slowest one).
To me it sounds like a very solid computer.
At least faster than average. The only major things i run in the background are McAfee 8.0 Antivirus and Windows Defender Beta 2 (MS AntiSpyware).
Usualle around 300 Megs of Memory are used (as shown by the task manager).
I Defragged the HD two days ago and use registry mechanic to clean up the registry every month or so.
Right now, as i am typing this, the computer is so slow that dragging the aim window around leaves a trail on the screen. Switching between mozilla and aim take about 3 seconds (thats pretty slow compared to what it shold be). This is all after i reststarted about 3 times and shutdown windows defender in the background.
This is not typical behavior but it happens too often to go unnoticed.
Another problem i have is a game called Midnight Club 2 (racing game)
Sometimes (usually) Its like a slide show. Sometimes it kinda like warms up and starts going normal after 15 mins of stalling, but considering that this game is a few years older than the laptop, that shouldnt be the case at all, should it?
Thats the only game i play (very occasionally) and i have like 2 other games installed (not used usually tho).
Other major things I have installed are Matlab (the process for it does not run in the background tho), MS Office 2003, MS Visual Studio 2003.
im pretty sure i dont have any spyware / viruses as i always run and update the needed scanners for that.

so any clue on why this is shuch a POS?

Thanks in advance.

thanks for the reply.

I guess thats the last resort (again, i reformatted in April, and installed only the mentioned software on it since then). I guess i'll have to try that if nothing else comes up.
another reason i dont think its spyware is because i checked out all unfimilir processes in task manager and they all seem legit.
As for the viruses - my computer was scanned for viruses after i reformatted and connected to my college network, and macafee was running ever since.

thanks for all the responses.

it stopped booting up so i guess i dont have many options left.
I dont recall how mnay processes were running, but that was definitely something i monitored and killed as needed.

actually what happens now is it turns on and goes to windows loading screen (the first out of the two i think) and after 5 seconds or so of that, it restarts itself. Im left the memtest86 to test its memory, hopefully it will be done by tonite and then just reinstall windows, get the needed documents and then maybe reformat and start clean.
thats assuming nothing is wrong with the hardware.

a little side note - man is that thing running hot.
the whole table is VERy warm after it sat on it for a night.
and the noise is loouder then the desktop.
but i guess thats normal looking at some of the other posts here.