I dont know about v8, but I just upgraded to v10 pro from v9 pro, and both of them worked fine with Vista Home Ultimate. I presume that 8 will work just fine too.
There are vista-specific(and multi-core support) updates for Samplitude under the support section on
www.samplitude.com I dont know your situation, but when I was *trying* samplitude to determine whether or not it was a good investment, there was a lot of functionality that I missed out on by not being able to d/l updates from support.(the updates are many and very helpful)
Good choice with Samplitude. I bought it and Sequoia a couple years back and wouldnt trade them for anything. There doesnt seem to be a thing that it cannot do.
Oh yeah..there is a very cost-effective version of Samplitude(LE) that was only around 50-60 bucks direct from the website.