Oh well, got Win98SE installed, the SB100 also installs fine and now also has the Q3D Display Properties Tab. Looking good so far.
Did some testing but basically everything going 3D failed (inlcuding the definitely working Radeon 7000 AGP) and eventually the System failed to boot all together
Turns out the Harddrive I used is toast, so I have to reinstall on a new Harddrive tomorrow.
--- edit --- Bad news, I can't get PCI cards to work reliably in the test System.
I finally managed to make the PCI 2D Card run (attaching or touching the VGA cable is enough to make the card freeze).
But : although properly installed I only get pixel glibberish from the SB100...
Might be it has the same problems in that system as the 2D card, might be it's toast against all expectations.
Anyway, I have to assume the card is possibly damaged and will change its status in the auction accordingly.
Due to that, recalls of bids already placed on it are accepted of course.