How recently has is started doing this? What version of Windows are you using? Is it up to date ( ie all Microsoft patches and updates applied)? What antivirus/ antispyware; are they up to date, and scans done recently? Free ones here if required click here click here
It's an issue with SpySweeper. You can either put up with it meantime until they release a new build, (they are aware of the problem), or, as a short term measure, go into Shields\Windows System\Windows System Shields and untick Active X Shield.
The latest Sun Java update can also cause SpySweeper to slow down IE but I haven't found that here.
If you do disable the Active X Shield protection, but are not too happy about doing it, you could download Flash and Pics Control from click here This will give you a toolbar icon in IE from where you can quickly disable/enable Active X, Scripts, Java, etc. i.e turn Active X off until you need it. (SpySweeper may warn you about this program as it's a browser extension but it's perfectly safe.)
Another alternative would be to Run Microsoft Anti Spyware click here in real time instead of SpySweeper, assuming you have XP.