iexplore.exe shows high cpu usage

It and explorer.exe together are gobling up all the usage (spikes to 100%, which sometimes lasts for 3 to 5 seconds). It happens everytime I click on a web page. I'm getting 15 to 18 mbps on cable but pages still load slower than I think they should. I use IE7, have XP SP3 and have an AMD Sempron 2200+. Is this a normal thing? I've ran scans with Avast, Spymaster and Malwarebytes and haven't found anything. I also reformatted and reinstalled XP about 10 days ago so it should be clean.