You have to be careful about the trigger voltage on the flash. Digital cameras won't tolerate the high voltages that old film cameras could deal with. For what it's worth, I recently wrote to Pentax to see what levels of voltage my DSLR would handle. They were very non-commital. Here's the response I got:
RICOH Japan has never released the trigger voltage specification for any of the PENTAX DSLR cameras. Older PENTAX brand flashes are safe to use on the cameras. These older flashes that are not P-TTL compatible have to be used with the cameras in manual mode. We do not test or recommend using third-party brand flashes with our DSLRs but if you are contemplating it we strongly recommend using a Wein SafeSync hotshoe adapter to protect the camera. Damage to the camera resulting from use of a non-Pentax brand accessory will void your warranty.
If you are in need of further assistance, please respond to this email or call our technical support center at 800-877-0155.
I opted to buy a Wein SafeSync for use with my flashes. Another option might be to use a wireless trigger to fire your flash, rather than attaching it directly by cable. There's a chart out there that lists the trigger voltages for quite a few flashes, but I don't have a link to it right off-hand.
Edited to add: Here's a link to that chart of trigger voltages.
Photo Strobe Trigger Voltages