OK, I've uninstalled the drivers that came with the soundcard and download/installed a newer version from scratch (but not the newest ones) which include EAX 4.
It seems to be working ok for now but if I get more problems I'll try the newest ones.
Thanks guys.
Just FYI Bifta, the EAX 4 update on the CD was not written by Codemasters, it's a proper Creative driver, which just saved me from downloading it.