I would go ahead an buy the 1 GB Stick for your iBook.
The original 512 MB DIMM in your iBook is permanently soldered in place, so
adding 1 GB to your second RAM slot is the best choice.
You'll be amazed at the performance improvement.
Installing your own RAM is a simple matter of making sure that the pins are all lined up properly and then pressing carefully but firmly to make sure it is properly seated in place, that's it.
Just make sure you follow basic anti-static procedure.
Apple has step by step directions posted on their web site.
I think PBfixit.com also has a how to posted.
NewEgg does have great prices, but you must know exactly what you are buying and they do not guarantee Apple Compatibility, You're buying specs only which is usually O.K.
but again, if you select the wrong DIMMs, you'll have to pay for return shipping and restocking.