I agree with your reticence in spending much money on the iBook.
How big is the hard drive and how much space remains available on it? If it's been awhile since you did any hard drive maintenance, you may want to try booting into
Safe Mode. This will take quite awhile longer than a normal startup because it does a file check and repair of the hard disk.
You will see your normal desktop. Once completely started up in Safe Mode, restart normally, and go to Applications > Utilities > Disk Utility. Click on the top hard drive icon in the left sidebar and note the
S.M.A.R.T. status at the bottom right of the pane. What does it say?
Select the named boot volume in the left sidebar ("Macintosh HD" unless you've renamed it). (This is where you can find the hard drive capacity and how much space remains available on it.) *Repair permissions on it.*
See if a little hard drive maintenance perks up performance.
I might suggest replacing the 128 MB RAM module in the one available RAM slot with a 512 MB module. It won't cost a lot, and you will see a bit of a speed boost.
http://eshop.macsales.com/item/Other%20World%20Computing/100SO512328L/
Instructions for replacing the RAM can be found here:
http://docs.info.apple.com/article.html?artnum=111918
Good luck with it.