Ever since upgrading to Internet Explorer 8, I

Ther are known conflicts with Vista and IE8 - particularly with Vista 64-bit.

I would suggest uninstalling IE8 and reinstalling IE7 or using an alternative browser such as "slimbrowser" (excellent program) or similar.

IE8 can be uninstall by using Add or Remove Programs module in Windows XP, but in Windows Vista, Windows Internet Explorer 8 is not considered to be a ‘program’. Instead, IE8 is categorizing as an ‘update’. Thus, users will not be able to find Windows Internet Explorer 8 in “Programs and Features” of Windows Vista.

To uninstall Internet Explorer 8, go to Control Panel, and click on Uninstall Programs link or Programs and Features icon. Then on Tasks pane on the left, click on View installed updates link. Locate and select Windows Internet Explorer 8 in the list of installed updates, and then click on Uninstall button. Click on Yes when asked that are you sure want to uninstall the update.

If there is no option of IE8 been found on “Programs and Features” or “Add or Remove Programs” dialog box, or uninstallation of Internet Explorer 8 is unclean (causing error message such as setup cannot continue because a more recent version of Internet Explorer has been detected on this computer when trying to downgrade to IE7), try to manually run the spuninst.exe.
To do so, go to C:\WINDOWS\ie8\spuninst\ folder (your drive letter may be different), and run spuninst.exe.

Restart the computer after uninstallation completed.

Hope that helps :)