what kind of Linux...
 

which distribution of linux do you suggest to install on P120/32M RAM/1,5Gb HDD?
I already tried Mandrake 8, RedHat 7.1, SuSE 7.1 but they work very slow on X (Video Card Cirrus Logic 5446)

your distro's are all fine, you just have a VERY old computer. don't use X, at leat not KDE or gnome. try blackbox instead

Get at least an other 32 Megs of RAM; that matters the most.
If you have 64 M RAM your machine will still not be fast, but at least it will not be unbearably slow.

Hi,
Using X in your situation is hard, but possible. Just don't touch KDE or GNOME! Look for other window managers (Window Maker, Blackbox, AfterStep...). And your system configuration should be a very good one. Don't install anything you aren't sure you'll need. It will be also good to edit startup scripts.

Mara