Why is my computer slow? It is a decent spec and It does not have any virus's or spyware/Malwar

I am wanting to get to the end of this but do not know how! My computer just seems sluggish and I just don't know what the problem could be.I want it to be as fast as it was when Ifirst installed XP if possible!

Here is some info about my computer

1024 mb ram - 160 gb hdd - pentium 4 ht (hyper threading) - 550w power supply - spire cpu cooler (heatsink) i think its for p4 775 - 64mb graphics adapter (is this poor even though i do not play games? ) - windows xp home service pack 2 - broadband connection (even though irrelevant to pc speed itself)

A few programs used on the computer

AVG anti-virus - Firefox - WMP 11 - Quicktime - Nero 6 - Spybot S%26E - BT applications for my broadband - IE7 - Registry Mechanic - Zone Alarm Firewall - Microsoft Office 2003 - Winamp

I constantly run checks for spyware and virus's on my computer but never find any, even on other software brands.

I want to solve the problem, as my pc's performance is not living up to.

I will appreciate your response

Why is my computer slow? It is a decent spec and It does not have any virus's or spyware/Malware!?antivirus protection

As a computer technician and having read through all of the other replys in this thread it would seem that the main problem may be the number of programs that are running in the background whilst you are trying to do other tasks.