The G3 version of iBooks MAX out at 640MB of ram (128MB built-in, 512MB chip in one open slot). They require PC-100 SO-DIMMs, however most PC-133 SO-DIMMs are backwards compatible (I'm running a 512MB one in my iBook).
1GB SO-DIMMs are only available in DDR based memory (PC2100, PC2700, etc.).
Trip, you're already maxed out. Only option is to buy a newer machine if you need more RAM.