So, I just bought a Canon Digital Rebel XTi the other day, and I have been playing a bit with it. One question I have, is whether or not the old Sunpak auto 433AF flash on it will work with my Rebel XTi or if it will cause problems. The flash was designed “For all Canon EOS cameras” but I believe it predates digital. Does anyone know of any way I could find out without actually test-firing a shot and hoping it doesn’t screw anything up?
Well, it looks like you won’t actually screw up the camera (http://photography-on-the.net/forum/archive/index.php/t-315066.html), but it probably won’t work in TTL model. If the flash has a manual mode, you can probably use that.
Ahh, your Google-Fu is strong, Sensei. Thanks a bunch. Now I just need to find a voltimeter to make sure my (much older) Focal brand flash isn’t going to blow up my camera. 
Why don’t you just ask Canon? Look here:
http://www.usa.canon.com/html/canonindex.html