> Intel Celeron M 420
I'd recommend against any Celeron CPU. It's slow and not energy efficient.
A Turion64 ML-<something> is OK but an Turion64 MT-<something> is more
energy efficient, so check the details.
W.r.t GNU/Linux support I've come to the conclusion that it's a question of
luck more than anything else. I'm pretty sure you'll be able to get Debian
running just fine, with full support for the main elements, no matter which
laptop you choose.
Stefan