Most likey the Addons that you have installed on your XP machine that may be slowing it down because when you open IE, it will also try to load all the addons you have installed.
In IE 8, just click on [Tools] then [Manage Addons] and disable all the addons that you don't use and see if that helps.
If it's still a problem, you may have to use HiJackThis (
http://free.antivirus.com/hijackthis/) instead. HiJackThis is really good at detecting all other addons and especially good at detecting Browser Hijacks.
Here's what you can also do:
1. Download HiJackThis, make sure there is no "iexplore" processes running in Task Manager (Internet Explorer) and then run HiJackThis.
2. Choose "Scan Only".
3. After the scan completes, look for items that has "BHO" next to it.
4. Remove the tick next to the ones that look suspecious (if you're not sure, Google is your friend). My suggestion is to just remove them all and then test if that improves the load time of IE. Then you can start Googling up what the BHO and IE addons are used for then enable them one by one.
Hope that helps.