Both chips are certainly overclockable. However, you have to take into consideration what sort of motherboard you have the chips plugged into (does the motherboard have PCI/AGP locks, does it have good overclocking adjustments for voltage and FSB settings?).
Plus, you'll need to have a decent power supply, and good cooling goes a long way. As for guides, I think several users around here have some, I just can't remember which. I'm sure someone here will be able to help you with a guide.
If you're good with the above conditions, you'll have ideal chances to overclock to close to your chip's max. What is its max? Nobody knows. It's different with every chip, as overclocking is never a consistent or guaranteed thing. I'd say your XP3200+ should get about 200mhz though. Your sempy I'll have to guess at 400mhz.