So I've bitten the bullet and ordered an ASUS Eee PC 901 W006 from Amazon.
This has 1Gb of memory, 20Gb of solid-state storage, and is preloaded with Linux.
All being well it will arrive tomorrow, and then I can try installing Lenny upon it. From the Debian Wiki it seems to be a painless process. I guess we'll see..
ObFilm: Twelve Monkeys