Through regedit. That's Start, Run, Regedit.
**WORD OF CAUTION**
Improper mucking around in the registry can turn your computer into a boat anchor (at least, until you reinstall the OS from scratch). Make sure you've got comfortable backups of everything before you get started.
**END WORD**
I have to add that in, because if you're asking how to get into it, you've probably never had that warning before [img]smile.gif[/img] Since you're on XP, I'd set a restore point just before doing any registry manipulation.
Once you're in there, do an F3 search for strings that appear to be related to the old printer. That would include things like Apollo and the printer model. When you find something, delete it. F3 to find the next one.
Don't go too fast. You've really got to read the entries it comes up with. I say this because it can get really, really boring...
I would go through the steps I outlined above before doing a registry crawl. The important thing is the reboot between, to ensure that any traces from the last time are completely gone. If you don't, they may still be in memory. And the fact that your current printer is USB doesn't matter much; it still has to get recognized.