Might I recommend the Gigabyte GA-P43-ES3G, it has 5 PCI, 1 PCIe x1, and 1 PCIe x16 slots. It has drivers for Windows XP, Vista, and 7.
It's socket 775, which supports the Intel Core 2 Duo and Quad CPUs. It's about the newest you'll be able to find that still offers that many PCI slots...