ibook Memory Question

Ok, I have a iBook G3 500mhz (Dual USB) with 256mb of ram, I want to upgrade it, I've heard they go as high as 640mb total. How can I tell how much I can put in mine without going out and spending money on something that might not work...

Any Ideas?

http://www.lowendmac.com/pb2/ibook3.html

or if you don't want to read your full specs:

"RAM: 64 or 128 MB of SDRAM soldered in place, expandable to 576 or 640 MB using one 1.25" 3.3V PC100 compliant SO-DIMM"

Next, shopping link: www.dealram.com (comparison shopping site for RAM)

goto www.4allmemory.com You select your computer model and they tell you what memory (that they have) that will work with it.