microsoft spyware i have been using it since came out and i like it.
Check start up in All Programs and delete any unneeded start up software in it.
Also run "msconfig" from the run box on start menu and stop all unneeded services and programs from running.
Also get into the Add/Remove Control Panel and take off any unneeded software.
Try using
Easy Cleaner it a nice clean up software for the registry. Remember always to a manual save point in system restore before messing with the registry.
A good free virus software is
AVG Free Edition
Defrag hard drive. Some say once a month I do it once a week it only takes about 4 mins (55gb) if you do it weekly.
I forgot to say
Intel Application Accelerator it is a essential bit of software for some Intel chips, one of the best bits about it is if you run the software it will detect if it is needed.
PC Answers is a good site for getting advice on getting the most out of your PC
You can always start again. I do it every 6 months. Just take copies of anything you want to keep and stick the Windows disk in (it says dell in big writing and widows in small) and reformat drive.
How much memory are you running? very often the cheapest and biggest fix a PC can get. I run 2 GB on my dell. If you need I will let you know what ram to buy (different ram for different things) to make the biggest difference for how you use your PC.
I like playing a online war game (Blitzkrieg) that has high demend on the system so i have to keep my PC well tuned to be able to cope.
When i got XP one of the most annoying things for me was Windows Messenger.
This will get rid of it once and for all.