If you aren't using the proprietary NVIDIA drivers I'd suggest compiling the
game again on Trisquel. Debian 6 is older than Trisquel 5.5 so whatever works
on Debian 6 should work on Trisquel 5.5 (generally speaking). As miga said
Debian and Ubuntu/Trisquel are not binaurally compatible.
I'm wondering if your mistaken though about not having the proprietary NVIDIA
drivers installed on Debian 6. The reason I'm thinking this is because you
say the Nouveau people indicated a lack of support for the card. That
wouldn't surprise me either. The newer cards which yours is don't have the
same level of support as the Geforce 9 series cards (9500GT for instance).
If this is the later case and it is a compatibility issue and this is a
desktop you can probably upgrade to the 9500GT. The 9500GT is the best card
to get at the moment.
https://www.thinkpenguin.com/gnu-linux/geforce-9500gt-1gb-pci-express-20-video-card-gnulinux
