It's not really a mod Sduibek, I put duplicated content that is unchanged in Fallout 2 (some art *is* changed, but not all of them) gets moved back to FO1 and I try to point FO2 content towards a master.dat and critter.dat folder instead of DAT file... then I try to make it load Fallout 2 stuff for the second game. I can't get that to work though, it's probably nothing like doing Fallout 1 in Mapper.
The firstest thing I did was to make both Fallout games point towards the same directory for music, which in my case would be "D:\INTRPLAY\FALLOUT1+2\data\sound\music". Then, I'd move the original Fallout graphics like for critters, backgrounds etc.. It kinda works, takes up less space...
EDIT: Oh, Lexx has something like this? I had no idea, can I see some pictures?