I think your best bet would be to try out the dd-wrt firmware on your router. DD-WRT Wifi Hack and UMA - Curve
There's a thread where it's being discussed and I took a quick look on the net and it appears people have had good luck loading dd-wrt and openwrt on your model of router. One caveat that I did notice is that some people had problems with it when using PPPoE connections, and there is a fix or workaround for that as well.
If your not comfortable attempting that, and haven't had luck getting the 8320 to connect after trying some recommended settings on this board, I'd say just watch for a good sale or get a t-mobile branded access point.