You can use a single graphics card for dual monitor setups. All modern cards have at least 2 connectors on them. Depending on your card, there will be a combination of 9-pin Analog (DSUB), DVI, or HDMI. You just need to enable the use of 2 monitors from within the control panel (Nvidia has their own control panel, not sure about ATI because I don't use their cards).
I am fairly certain there are no 775 boards that support DDR3 use. Any board can be made to use USB3 using a PCI-e addon card though, and the majority of motherboards will offer multiple PCI-ex16 slots.
Have you considered upgrading to LGA 1156/1366?