Here's a link to the basic layout of your mobo:
Check it against your mobo. Look to see if there is an additional port/slot between #15 and #16 that is off-set from the others and is a different color (possibly). If it does, is it plugged or open?
"Your system has two connectors for installing memory modules that provide up to a maximum of 512MB of system RAM."
IBM is stingy with their technical specs. There's not much more than this. Here is the page of page of links for Parts Information:
Hope that helps. I couldn't find what the maximum CPU it could handle was. If you dig, you might come across it, 'cause I just probably overlooked it.
EDIT: I think the site said that there was a BIOS update for your computer. Your model is 6018-UP7.