B4 you start here are a few things to do that will eliminate 90% of the time to reinstall. If a bubble appears at anytime saying these files are hidden "open" them.

From the administrator account on the start menu select control panel, then click administrative tools. On left side choose disk management, your hard drive partitions will display. Right click your "C" drive and select shrink partition, accept the maximum amount. If it will shrink create another partition as large as possible and name it "storage" an accept windows suggested drive letter designation.

Now on the start menu right click on Documents / Properties / location, now designate the storage drive letter where the documents files will be located. Choose "OK", move to or apply and yes your sure or whatever gitr done. Repeat for "Pictures, Music, Videos, etc.."  Now when you click on Documents etc. Windows will access the file in the storage partition.

Now reset the page file; on start menu right click computer / properties / advanced / performance - settings / advanced and select "No Page File" / it will ask and yes you are sure. Reboot and reset the page to equal the amount of RAM - each GB = 1024MB, apply.

Go to start menu / left click computer then right click the "C or windows" drive / properties / select "disk Cleanup" then put a check in each box represented / then click the button at the lower right corner, yes you want to delete all instances of system restore, after this completes select delete. Reboot, defrag 2x then reboot after each defrag.

Now insert the Vista install disc and reboot, reinstall vista to the windows drive, this will not disturb your files in the storage partition. 

If in the future a virus occurs it will be confined to the "C" Windows partition and not your files unless you save a virus to your documents etc..

Cheers!