Presario 1200 US upgrade

I was very fortunate to trade my very nice, new, expensive laptop for a
Compaq Presario 1200 US* which has a very slow Celeron chip and very
little memory, 128mb is soldered in and 256mb was added making a total
of 320mb. Believe it or not, the thing is capable of doing what I need
done, I use it mostly for checking email when travelling.
It would be nice, however, if I could add a bit of memory. I figure
putting a 512mb module in place of the 256mb module would give me more
but everything I read says 320 is max.....

Anyone know of a way to increase the memory size or does anyone know
for sure what will happen if I did put a 512 module in there? So far
my answers range from "Nothing, it won't even boot" to "It will explode
with enough force to end all live on earth". Some how I think both
answers are wrong?

Any help would be appreciated, again, it does what I need, I'll
probably keep it no matter what but it would be nice to speed it up a
bit......

Oh, BTW, I'm running XP Home if that matters at all, and I have used a
bunch of tricks to speed the software up but I'm up against hardware
limits.



*My kid, the con-artist, convinced me he needed an up-to-date laptop
more than I did. sigh