The tool .Process Explorer. in sysinternals will be of great use if you are with Oracle on Windows. In *Nix machines one could see all the process using ‘ps -ef ‘, but how about in Windows. Its here this will help you.
Once i had to apply a patchset on Oracle 9i in Windows 2000, i did ‘stop’ all the oracle service n all from the Service. When invoked the setup.exe, it said that one file is being used by some process. I was perplexed on how to find out which process was using the file and this tool came in handy and it showed that it was some scanning application by CA which held the oracle file. I just killed the CA process and went ahead installing the patchset. [Ofcourse, you need admin privilege for this]