Will GUIminer use CPU as default if it can't find OpenCL? Otherwise, I'd assume I'd have to change a setting somewhere but I can't find where. Under Device it doesn't even give me an option for CPU, it just says "No OpenCL Devices."
I don't know much about GUIMiner, but I don't think it can use a CPU.
When I used to do CPU mining I used jgarzik's CPU miner. It seemed to work pretty well.