IE7 loaded in under 1 second.
IE8 was extremely slow loading, and opening new tabs.
IE8 was taking up to 8 to 10 seconds to open on my 2.40 Gig Quad Core, 4 GB, Ram Vista system until I did an 'Immunize Undo' backing out the immunized items.
IE8 loads in under 2 seconds with Spybot SDhelper off and Immunization
If you immunize the the Hosts file, IE8 startup slows way down.