I'm using "image resizer", it's a powertoy from microsoft. VERY easy in use (just select ALL the files you want to resize in explorer), right click on them en select resize. then select the size you want (640*480, 800*600 or 1024*768) and GO
The program makes copies of the original files (though you can choose to resize the original files)
resizing in less than a minute.
just google for "powertoy image resizer"
