Yes, Vista is a supported client OS for 8.7 and 8.8
The only thing to watch out for at the moment, is that SP1 for Vista is NOT supported yet - we're hoping to include that in SP1 for 8.8 and SP6 for 8.7 that are due for release in the next couple of months.
LANDesk EMEA Technical Lead.
We run the 8.8 agent on several Vista SP1 machines and haven't seen any issues related to Vista or SP1. Do note that LANDesk doesn't support it,