in general normal stuff should work. really you need to just start testing the apps and find out.
heck there are a lot of things that a "vb6 app" might do that could be an issue and you have to know what the app does.
for example: trying to write files in folders that apps are not supposed to use. in say windows 95 or windows 2000 the app generally worked .... but in vista or 7 the same app would have issues.
vista will be more in-your-face about it. in fact i would even say test the app with vista ...
if it works there then 7 should be fine.
if vista complains see if it can be updated to fix it.
if not you have two options:
1) application compatibility settings
2) xp Mode - the virtual pc running xp that is a free part of windows 7.
app compat settings: as i recall there is a tool from MS to help with creating a profile to run the app on the new os with some settings to "smooth over" some issues.
if all else fails XP Mode can run a lot of old stuff and to the user it looks like they are not even using a virtual machine other than the "window chrome" is the XP style.
That's good to hear. Generally, we should be fine as most apps don't write files. Some do make reads/writes to HKLM, which I assume will need UAC elevation.