It depends on the card, as marmasatt explained. The only Geforce cards which don't need the internal SPDIF connection (2 pin audio cable) are the recently released GT 220 and 210. All Radeon HD 2000, 3000, 4000, and 5000 series cards can pass audio over HDMI. Most newer Geforce cards should at least offer the SPDIF connection, but if they don't then you can't pass audio over HDMI, so be careful.