Your GTX 295 doesn't have built in audio capability, but it may have an SPDIF in connector. Your motherboard should have a SPDIF out, and with the right cable you should get audio out over HDMI. Of course you have to enable digital audio out in the appropriate control panels as per usual. Audio will be limited to stereo or AC3/DTS passthrough. Here's a guide.
Q9400@3.2GHz | GA-P35-DS3L | 8GB DDR2-800 | MSI GTX 560 Ti | Lian Li PC-7B | Corsair 450VX | Dell 2005FPW