I know its not exactly the solution you're looking for, but its honestly a better way to go.
when a browser resizes an image it tends to distort, if you actually resize them to the size you want to display, you usually get a better result.
I use a program called irfanview to resize everything before I start uploading products. you can get it free, just go to
www.download.com and search the name.
once you install it and start the program, hit the B key, and it pulls up a menu to do a batch resize...you can resize an entire directory of images, and write them all to a new filename in a new location. Its quite easy and useful.