One of the options below should work for you:

After installing the application on the Vista machine, right click on "Command prompt" (found under "Start" button -> "All programs" -> "Accessories"), then choose "run as Administrator"

At the command prompt (the black screen that comes up) type

regsvr32 /u /s xxx (where xxx is the name of ocx or dll you are having problems with)

Press enter and this should bring back a message saying it was successful. Leave this black screen open and try running the application again. This may work for you.

If not, go back to the black screen and type

regsvr32 /s xxx.

That should do it. Some versions of Vista require some ocx's/dll's to be registered under the Administrator account.