In theory, yes. If you have bad luck , your machine does not "like" a certain RAM module, though. There is, however, no risk in trying a PC2700 module in the iBook. You will not get any performance boost, as the PC2700 module will be runnning at 133 MHz.
disclaimer: lexfuzo is by no means responsible for any damage you are causing to your machine by experimenting with RAM upgrades.