Two sticks of memory are currently in there, both 128mb and the max it
will support is 512mb.
I didn't search for very long, but the info I came across
contradicts this. It appear to have came with PC2100, that it
can support at least 512MB per slot for 1GB total (assuming it
only has two memory slots).
Main question is, are you inclined to upgrade the system anytime
soon, so that any memory you buy might be reusable in next
system, IF you bought high enough spec memory? You could buy a
256MB PC2100 module, or two, but IMHO, you might be better off
buying a name-brand budget grade of PC3200, single 512MB module,
which would likely be viable for use in the next system if bought
within the next year or two. Granted there are no guarantees
that the industry won't have shifted to DDR2 by then, but
certainly DDR(1) components will still be available and PC3200
isn't that much more expensive than PC2100.