Generally speaking, you should not worry about installing Win Vista or Win 7 on an older laptop (unless it is ancient) since those OSes will have legacy drivers. Installing Windows XP on a current laptop is a different issue due to potential non-existing Win XP drivers for motherboards.
Win 7 is preferred over Win Vista due to less annoyances. But if you already have a copy Vista, then you might as well try it out before you buy Win 7.
Backup all important files to either an external hard drive or a separate partition on your hard drive. If you are going to completely format your hard drive (meaning the partitions as well), then it's best to backup your files to an external device.