Thanks for letting us know. When installing Sitefinity under Vista you should consider the following issues:
Please, try to uninstall and install again Sitefinity. After the uninstall complete check if there is something left in Program Files/telerik/Sitefinity3.0. In case there is, delete the folder manually.
Hoping there won't be problems this time. Let us know instead.
All the best,
the Telerik team