Well known joke is to open/close cd-rom tray. But also the great thing is to make floppy drive to grunt. When no diskette is in, try to refresh directory contents of floppy drive (issue dir a:\* command)

Some people can't understand that it is bad to download many unnecessary data from inet especially when your organization has poor channel. Ok, let them do it. Suspend (this is the most safe way) all threads except first one of downloading program ;)

Deletion of the hklm\software key from the registry. Discovered accidentally when we tested GUI client under Win9X. Great results. Programs slowly fail and when system is restarted, it shows installation screen and asks for a serial number. You can enter that, the installation will try to continue...