I couldn't even insert the GB carts into the DS.
I didn't force them though, they just didn't seem to want to go in.
the back corners need trimming have a look at the shape of the carts
The DS doesn't have the right chip in it to play GBC/GB games, the GBA did. That's why the Micro could not play GBC games, because they couldn't include the chip if they made it that small.
This could be overcome with emulation
Although the whole idea of sticking a GB cart in an NDS seems pointless to me when you can stick 100's of GB GBC roms on a smaller flash device even standard GBA carts are too bulky in a DS lite it reminds me of the days when i used to use a Mastersystem adapter on Gamegear I still have it and a copy of R-type but theres no way i would waste my time using it.
The most obviouse reason Nintendo have not included GB support is so you buy the games again for a crappy virtual console.