1. Get P35 Motherboard, although it work at PCI-E x16 1.1, you can run 3870 on that.
2. Get GA-EX38-DS4 as reddivil6 said
3. Wait until the end of May. New Mobo with intel P43/P45 chipset, which support PCI-E x16 2.0, will be released (if ther is no delays)