Personally, an iBook G3/G4 running Panther/Tiger is decent enough for taking notes, Excel, spreadsheets, internet, basic photography stuff. If it has atleast 40 GBs of HD Space, and 512 MBs of RAM, I think that would be decent enough.
I am a Freshman in high school and had an iBook G3 Clamshell 466 MHZ, Combo Drive, 320 MBs of RAM, 40 GB HD, running Jaguar (Mac OS X 10.2). I then got a first generation BlackBook in May 2006 from inheritance, the Uncle died about 2 days after buying the MacBook and I got to get it. I didn't use it for about 2 weeks after receiving it because I was tranced from the event, so I couldn't return it. I decided to keep it. I gave the iBook to a friend for a birthday present. The MacBook had numerous problems and after receiving 3 more MacBooks to replace it, they gave me a MBP for free. Even the MacBook was overkill, and now I even have more overkill. The iBook was wonderful, had a brand new battery so it lasted about 4 - 6 hours. It was more portable, more durable, and I wasn't afraid to bump it. I could run iTunes, FireFox, and Word all at the same time without much trouble.
You could easily buy the iBook I had with the same specs for 200 dollars shipped. It is better for a high schooler, that way, when you get to college you can buy a brand new, spanking top-of-the-line laptop for your whole 4-5 years of college life.