Don't upgrade if you are uncertain. Create another partition on your hard disk. Shrink the Vista partition if needed. You need to give yourself about 20 gbs, but more, if you can spare it, for your software.
Give the new partition a distinctive name, so you make no mistakes (WIN7?)
Boot up on your install disk and install 7 in the new partition. It will set up a dual boot, without disturbing your Vista installation, and you can enjoy both.