"Instant on" PDA like Linux web pad or tablet PC

Hi!

I am looking for a PDA as possible in web pad or tablet PC size,
running e.g. with Linux.

Do You know a good start for searching on this subject? (I did a lot
of research already, but I didn't get happy with this until now :-( )

I am looking especially for following feature: "instant on". This
means, I do not need a tablet PC with Linux which needs to boot before
I can make notes and stuff. That is, indeed, what I couldn't figure
out until now: how to do this with Linux, better: which PDA-OS-like
Linux is good here?

I know, I will do some more research, but I hoped you got some nice
beginners entry page or even experienced stuff :-)

CU!