I suspect you've run out of hard drive storage space rather than memory. Unless the hard drive has previously been upgraded, the first iBooks only had 3 or 6GB hard drives, and like the later iBook G3 and G4, it's not easy to replace the hard drive. It's a complete strip down unlike the later Macbooks. The clamshell iBooks use 2.5" ATA hard drives.
This iBook used PC66 144 pin SO-DIMM RAM.
Sorry, not with the original stock hard drive. Your iBook was likely shipped with OS 8.6, for which there was ample space. Long ago I can remember upgrading hard drives in these as users moved to OS X, but the 800 x 600 resolution wasn't ideal. Later iBooks were more versatile and had 1024 x 768 pixel displays, but even then, the first white iBook G3 only had a 10GB hard drive.
Hi, and welcome to Apple Support Communities.
What is the hard drive capacity, and how much space remains available on it?
Do you have the original system CDs that came with the iBook when it was new?
They would include Mac OS 8.6.
You didn't say anything about having updated the firmware on the iBook, and that needs to be done before upgrading to Mac OS X. You have to do the firmware update from Mac OS 9.1 installed on the computer's hard drive.
(Maybe a previous owner updated the firmware.)
With sufficient hard drive space and Mac OS X 10.3.9, you should be able to use Microsoft Office 2004 for Mac:
Replacing the hard drive is not an easy thing to do: