The OS here, should be a properly licensed XP/sp2. Uninstall Yahoo! or Google toolbar, along with any other browser add-ons, to eliminate them as potentially responsible factors. Disable pop-up blocking in IE 7 along with any other features that may clash with certain web [site] implementations or practices...
Verify that your machine is malware free by running AV/anti-virus and AS/anti-spyware scans, ensuring that active AV-AS protection is enabled and that adequate firewall protection is in place. Finally, make sure your OS and other important software are fully updated.
note: make sure any security software you're running isn't conflicting with IE, e.g. duplicate pop-up blocking, etc... Modify configurations accordingly if this is the case...
If the sporadic hangs disappear, go ahead and re-enable IE features as desired, re-installing any desired add-ons such as search toolbars and the like, as well. If the hangs re-surface at any point along the way, utilize logical fault isolation to locate the offending element, and then post details on Yedda for a solution.
If the problem persists despite having implemented the above measures, then post additional details of your current situation, and we'll take this diagnosis to the next level....
