Trust Gamer Mouse vs D1X-Rebirth. Can't use buttons <- SDL problem?

I’m trying to get my Trust Gamer Mouse Optical GM-4200

to work in D1X-Rebirth

under Win XP SP2 which uses SDL but no matter what function I do assign in the
Windows Mouse Configuration menu, I cannot get the thumb buttons to work at all
in D1X-Rebirth. Any suggestions? TIA!