@Juvefan
There will be the odd game that still refuses to work using the 2 mouse button routine as described earlier. This problem can be (hopefully) alleviated by getting hold of a 'downgrader' like Relokick which loads a 1.3 ROM to fool the game into thinking the A1200 is an A500
This solution is not a 100% guarantee though, which again is where WHDload can help.
If it helps any, I've got a list of my games and how I got them working on my A1200 ... PM me with a valid email address and I'll send you it.