X on AcerNote Light 370?

I use a AcerNote Light 370, 16M RAM, Pentium 133mHz

How do I configure X? Is there a way to change the default wndow manager after boot-up? I can run X, but is horribly slow and only twm can run. Can I run xfce on 16M RAM?

Now, I get "You passed an undefined mode number", and when I pick one, all the letters and the whole screen area shrinks to about 2/3 of the screen. I tried using fb1024x768, but doesn't work now. Used to work.

Thanks in advance