SDPaul, welcome to the forum.
If you don't already have a full copy of Vista, I suggest using Win 7 64-bit. In my opinion, it is a far superior OS. However, before you buy any version of Windows, here are the Win 7 Upgrade Advisor and Vista Upgrade Advisor. These will tell you if the computer can be upgraded.
Here is the Software & driver downloads page for the computer. You can choose an OS from the drop-down menu to see which software and drivers are available.
Please click "Thumbs Up" if I have helped you and click "Accept as Solution" if your problem is solved.