Take a look at this:
http://www.dansdata.com/askdan00001.htm
32 bit apps will still run (vb6 apps are 32 bit). Overall, since vista is a new OS, there will be problems in some applications. 32 bit as well as 64 (although vista 64-bit will probably have more).
So in general, yes vb6 apps will run.
old windows 3.x apps are 16 bit and they will not run.