Will 32-bit PCI 2.1 cards work in 64-bit PCI-X slots?

I have a SuperMicro SuperWorkstation 5033C-T system that has 3 64-bit PCI-X slots. The only thing that I have found designed for PCI-X slots is Network Interface adapters. The unit has 2 Intel Pro 1000 integrated NIC’s that work great. Will standard PCI cards work in a PCI-X slot? I have noted on the manufacturer’s website that the standard PCI slot is 3.3 volts whereas the PCI-X slot is 5 volts. If not, are there any other expansion card types that have PCI-X support (ex. Sound Cards, TV Tuners, Graphics Accelerators, etc.)?