Not sure about xp, but in 98, if you have 2 printers installed you must actively choose which one you are about to use before you start to printt. You would go to settings/printers and right click the chosen one and make it default. Sometimes in some programs, you get a drop down menu, from which to choose, but not always.
Just one question canal6, you posted:
"Any idea why they won't cooperate individually no problem if both fitted only the Epson works"
and I'm not quite sure what you mean. Hope this can help.