I was able to solve the problem as follows:
1. Install the program with the installer
2. Copy the installed program components to a temp directory
3. Uninstall orov
4. Copy the files from the temp directory to for instance c:\orov
5. copy toolbar2.ocx to c:\windows\system32 (You need elevated rights for that)
6. Open a Command window (cmd) and run as Administrator
7. cd c:\windows\system32
8. Regsvr32 toolbar2.ocx
Added some clarifications and screendumps as requested by commenter Armand.
Recently Orov suddenly stopped working for me (probably a Windows Update messed up).
The symptoms look like a problem the author documented on his site.
The author of the program has some info on this, but the offered solution seems not to work on Vista.
I recently bought a new PC wit Vista Home premium. Installed OROV again and it works perfect again.