stitch: yeah it would be really impossible to get enough real licenses to do that. The only reason I'd prefer to preinstall it on those would be because honestly old PCs run quite well with well-configured Win9x installs, and sometimes lightweight linux distros can be hard to get working, i.e. Lubuntu, on extremely old hardware.
But in the event that I do that I'm thinking I'll provide working Win9x drivers, and have Lubuntu preinstalled, and leave the option open for the buyer to use Win9x, or another OS. I mean if anyone would voluntarily buy an old computer they'd probably be a computer enthusiast anyway... or extremely cheap