I installed 10.5, and indeed it helps a little bit, but I guess it's just enough.
in 10.5 I can use 1.8 GB of the ram installed, instead of 1.4 GB in 10.6
It's still not the 2.8 GB I would like to use, but ok.
Not really happy with downgrading my OS, but if this is the best way, I'll do it.
thanks!