DSL

What do you do with a 433 MHz Celeron, boasting 4.3 GB of storage, which you bought in '99 immediately after getting married and becoming impoverished?

Load a Damn Small distribution of Linux onto it. (This assumes you don't want to tinker with TinyOS.)

This machine (with fluxbox managing windows) is now more-or-less as responsive as the laptop running XP with 1600 MHz and 512MB of RAM. That's not based on any benchmarks or anything (someone link me an easy-to-run benchmark for basic throughput); just the usual open-firefox-and-surf-around-a-bit and see how it feels.

Also, at <60MB it can be fully loaded into even a modest RAM chip, at which point you can expect it to smoke the XP box and the Gentoo as well. I've gotta try that. I think the last system in which I pulled that off was a Mac SE 'round 1988. I remember that it rocked.