Just to clear up some confusion:

You can fit up to 8 32Mbit game on 1 256Mbit Flash Card. Because the Flash cards are MEGABITS, not MEGABYTES.

When you are backing up your own game onto your PC, then it will of course show up in MEGABYTES.

For example: Mario Adavance is a 32MegaBit game - so when you back it up onto your PC it will show up as a 4 MEGABYTE ROM FILE.

To find out how many MEGABITS your game is, just look at how many MEGABYTES it is, and then multiply it by 8. So 4 MegaBytes works out to 32MegaBits, and 8 MegaBytes would be 64 MegaBits.

And the flash card is 256MegaBit or 32MegaBYTE allowing you to fir up to 8 games on there maximum.

Hope that helps. Info was taken directly from http://www.gamegizmo.com/gba.html