Thank you so much for you help, and I'm sorry for asking dumb questions.... I can get the bracketing set under the CHDK menu although I 1) cant figureout hose to set the delay and the shot count, and 2) can not get the bracketing to initiate when I push the shutter.
Ahhh, sorry, but: IMO the SD300 don't have an custom timer mode, only a self timer mode with 2 or 10 seconds delay...only newer cameras (from the SD400 on) has the additional custom timer mode..
So set up the bracketing in CHDK menu, leave <Alt> mode;
then switch to the camera's
continuous mode , now xou should see your CHDK bracketing values on the screen.
Press & hold the shutter until the needed images (3,5,7 or 9) are taken, then release the shutter button.