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 (sdljoytest.sourceforge.net) 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