There are others but your post didn't tell what antivirus suite you installed.
I'm using XP Pro SP2.
I'm using Office 2007 Pro on my laptop. If I start Excel and load a spreadsheet from within Excel, it opens faster than a speeding bullet.
If I click on the same spreadsheet icon (on the desktop), with or without Excel open, it takes forever to load into Excel.
Excel starts quickly.
All patches are applied. Full in-depth spam and virus scan just done in safe mode.
Very few files or folders on the desktops, mainly shortcuts to other folders on D: drive.
Can't see any unusual processes running.