Newegg.com - ASUS P7P55D-E Pro LGA 1156 Intel P55 SATA 6Gb/s USB 3.0 ATX Intel Motherboard
Make sure your ram speeds are supported...and that you have enough sata ports, etc. Also note these pcie x 16 slots will run at x8 speed when two cards are plugged in, making each card run at half its potential speed. There will be a large performance increase, but not as good as two x16 slots...which I couldn't find.
If you plan on getting two at the same time, I'd recommend getting a newer card because there will be greater performance and less heat...
Asus P5Q Motherboard * OC'ed Intel Core2 Quad Q9400 2.82ghz w/ Arctic Silver 5 * OCZ Platinum 4GB (2 x 2GB) DDR2 1066ghz * Kingston Hyper X (2x2gb) DDR2 1066ghz * EVGA GTX 560 Ti Superclocked * Ultra X-Blaster ATX Mid-Tower * OCZ Vertex 2 120gb * WD Caviar Blue 500GB 7200 rpm * OCZ ModXStream Pro 700W Modular PSU * Sony Optaric DVD Burner * Windows 7 Home Premium 64-bit * 22" LG Flatron W2252TQ LCD * LG Flatron E2281
Samsung Series 7 17.3" Laptop w/ 256gb Vertex 4 SSD