All I have found so far is
mirascanv403u10.exe which one person says is what originally came with the scanner (at least that's the version that's on his cd)...
Unfortunately I can't get it to start (as I don't have a scanner) so I can not make sure it's not the one you have (the numbers do seem to match, but it could be a different version)...
But I have found one way for you to save the images as .jpg instead of .bmp.
Use ScanButton 3.0 (which if you don't have comes with the version above).
Choose scan to file (the rightmost icon the on ScanButton toolbad), and when you select where to save the image click where it says "Bitmap files (*.bmp)" and instead choose "JPEG (*.jpg)".
That should at least save you a lot of space...
If that wasn't too clear, there are images which explain it if you start ScanButton 3.0 and right-click on the top of it (opens a menu) then choose "Help". When the Help funcitons opens up, click on "Get Start" and "Scan to File".
Hope this helps you a bit, since it's all I've been able to find so far...