i've just barely have a driver from the usb incarnation of marvell's libertas hacked together. as in i can boot over it (with hardcoded association) so long as i don't load the kernel over it (apparently openfirmware doesn't reset it when finished). it's not really in any sort of shape to have people looking at it, but if folks are playing with olpc stuff it's at contrib/tristan/libertas.tgz (you'll want to change some things in doassociation (and it'll be nicer if your ssid is 11 bytes long)).
enjoy, tristan -- All original matter is hereby placed immediately under the public domain.
