I just timed it exactly and it's around 5 or 6 seconds total on this Vista machine.
Was your Vista machine that slow on vBulletin?
I'm now at work on a Vista machine w/dual-core and only 1GB of ram. It's faster than that. But you're describing my W2K machine to a tee. It takes around 6 seconds/page, and that's before I open up 5 or more tabs after which my CPU is totally max'd out and everythying slows to a crawl. 2G RAM at home.