Are you asking if you can upgrade to Vista Home Premium?
I've never dealt with Vista but if it is like Windows 7 then go to Control Panel > Windows Anytime Upgrade and it should tell you your options and prices. Generally buying directly from Microsoft is cost prohibitive and you may find it cheaper to buy upgrade to Windows 7 Home Premium using a system builders copy and do a fresh install.
If you are asking about upgrading to W7 starter, I'm pretty sure there is no STARTER upgrade path, so again buy a system builders copy of W7 Home Premium and do a fresh install