Hi, Ellie.
It kind of depends on the size of the hard drive. If you get a 900 MHz iBook, it will have a 40 GB hard drive, and Tiger may work okay with it, but just barely. You really won't see what Tiger can do until you step up to a G4.
I left my 800 MHz G3 iBook with its 30 GB hard drive in Panther and upgraded to a G4 iBook to get Tiger. Others are comfortably using Tiger on their G3's, but I decided I didn't want to push mine with it.
You can keep an eye on the
Apple Store's Special Deals page for a fairly good deal on an iBook G4, but you're not likely to see a G3 there. Apple pretty much considers them obsolete.
The iBook G3 (Dual USB) has been rather notorious for
logic board problems, so that's one more reason to step up to a G4. My 800 MHz iBook G3 has been back three times for the logic board repair. On the other hand, there are many G3 owners out there happily iBooking away, oblivious to the fact that others have had problems.
I've bought four iBooks on eBay, but there are a lot of clunkers there, and you really have to know what you're doing. Don't buy any iBook anywhere that does not include the original software discs that came with it. This leaves out a lot of online stores that sell used iBooks, because the software Install and Restore discs are usually not included with them. You need those discs for hard drive maintenance and to reinstall and/or restore your software if you have problems with the hard drive. If you buy one without those discs, you can plan on having trouble getting them when you need them. Sometimes Apple has them available for a fee, but you can't depend on that.
If you live close to a college, you may find a student selling his/her iBook on a college bulletin board or in your local newspaper in order to get the money to buy a new computer. Students are rather notorious for abusing iBooks, though, so make sure you get a good look at it. Often the fact that a person has kept track of the software discs is a good indication of how well they've taken care of the iBook, too.
If you do decide to buy on eBay, make sure that your seller has only one iBook for sale (scammers often have half a dozen up at once), that it includes the original software discs that came with the iBook, that he/she has a feedback rating of 30 or greater with 100% positive feedback (or very close to 100%). Check out the feedback comments. Only buy from someone who accepts PayPal, and use your credit card to buy it through PayPal so that you can dispute the charge if the iBook is not as advertised.
Check out the specs on all iBooks at
EveryMac.com to see what is the oldest system you think you'd be satisfied with.
Good luck.