Digimag: I also had these problems with poclbm. It seems that it creates an .elf binary with every run, and there is something wrong with it. Just delete the binary (rm *.elf) BEFORE you run it and it'll be fine.
It worked for me! Thanks
If you do get it running let us know how and if it performs better than Diablo.
Unfortunately it doesn't. DiabloMiner performs at around 5 Mhash/s and poclbm at 3 Mhash/s.
DiabloMiner wins on a MacBook Air!