QNX has limited support for network cards. Probably yours isn't supported.
I highly recommend a DEC Tulip based card, like the Netgear FA310TX. They are $20 - $30, support 100BaseT, and are well supported under Linux, Windows, OpenBSD, FreeBSD and QNX (probably others too, those are just the ones I run). I have 4 or 5 of thses cards.
If you want to go on the cheap, you could probably get a NE2000 compatible generic card for like $10, which should work under Most OSes, including QNX.