I'm thinking about a low-end, away-from-home, maybe at the stable, machine. You know, check in on JavaRanch, compile a little Java code, check email, nothing too taxing.
I think some of the new linux "netbooks" are kind of fun looking (Acer, Asus, HP, and so on), but I'm also thinking of getting a refurbished 12" iBook (maybe 512-640 mg, 800mhz). In general, I'm trying to stick around $400-$500.
So, the iBook is old, and heavier - but it's also 10.4, Java is already loaded, etc. A new "netbook" is, well, NEW, but I'd have to brush up on Linux, load Java, etc.
Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)
I wouldn't consider "loading Java" being an issue. I think I'd be more concerned about that old machine keeping up with 10.4 (I assume you meant Tiger?) and how that (lack of) performance balances the learning curve of Linux.