Another thing you can do is to use a different background color, flatten the image, then select all pixels of that color with 0% tolerance and fill with FF00FF. You'll get the same jaggies, but you get to control them.

Or, create the image with no background color (ie, leave that part transparent) and save as png. If you use a module that supports per-pixel alpha, it'll be transparent without jaggies. (but only on Win2k and above)

Supersampling doesn't help, as the pixel with either be transparent or not with magic pink transparency. Magic pink pretty much guarantees jaggies against unknown backgrounds unless all your edges are straight and at right angles.