2001.10.10 17:17 "Re: Resizing Image", by Peter Montgomery
Check out this site:
The code is in Delphi (Pascal), but the source is available. Actually, the work is based on a chapter in one of the Graphics Gems books. You can find all of the Gems code here:
BTW, the method to use is resampling with a sinc filter if you want to do it correctly. All other methods are inferior to greater or lesser degrees.