Are there any tutorials for writing software for GB ?
Check every page on the GB Dev web ring first. Many good sources of info can be found on the ring. If you are programming in C using GBDK check out the GBDoK tutorial. Also check out the GBDK page & 420 Studios while you are at it. If you are programming in GB assembly language then locate Gameboy Assembly Language Primer (GALP) v1.0 on a web page on the GB dev web ring.