May also depend on the version of windows. I'm doing this on an ME machine and it's much simpler that Win2K.
Not for the faint hearted, Engineer, (but I don't think you're one of those), it is possible to do this empirically.
If you edit with regedit.exe, run searches on the name of the software house (eg Deerfield) and then on the name of the application (eg Wingate). Each time delete the key or the contents of the sub-keys that contain the names.
You're looking for Software keys or "Run" or "Open" keys in CurrentContolSet or ControlSet01 or ControlSet02 or somesuch.
Don't overdo it and remember the maxim to "quit while you're ahead" You will inevitably leave some detritus behind in the Registry but as long as you don't get any error messages about files not found you'll suffer no harm.
Sometimes you are denied access to a Key. Change to edit with regedt32.exe (Windows 2000) and you can change the attributes of the key and then delete or change it.