Alpha Blending w/ direct drawing pixels

Um, if some one could be so nice as to remind me how to do alpha-blending w/
direct pixels draws. I know I’ve read about it before, but I can’t remember
how to, or where to get that info. I’ve been scouring the archives, but w/ no
results as of yet. Thanks all

(Note, this is to get rid of the annoying resolution dependant background
images for SDLJoytest ( so if anyone is feeling
ambitious, feel free to hack away at the cvs files)–
"They that can give up essential liberty to obtain a little temporary safety
deserve neither liberty nor safety. "
–Benjamin Franklin