It's always a risky proposition, but you can just slap the stuff in there and let Windows figure it out, with one notable exception. If you are changing away from an older mobo meant for a AMD chip with a Via chipset, you have a higher probability of running into problems. You can minmize this by going into device manager, and removing all devices related to the mobo (motherboard resources, etc), but NOT the advanced power management, or plug'n'play BIOS. Do not restart the computer when prompted. Remove them all, and then shut down. Then swap your parts.
All that being said, a clean install would be preferable. If you're coming off of an Intel platfrom, though, you should be fine.