If it's happening the day Vista releases then Ubuntu Edgy Eft should be out (scheduled for October IIRC), and maybe even the release (or a few releases if things keep going the way they're going) after that.
(BTW, the next release of Ubuntu will be 6.06 (can't think of the codename ATM) and will be out in June. After that it'll be Edgy Eft, which the main guy (Mark Shuttleworth I think his name is) has said he's not placing any restrictions on what goes in it. There'll be some experimental stuff like Xgl (the X server built on OpenGL, or something. Well, it can do some pretty cool wobbly window effects and stuff anyhow.) and virtualisation (or at least, there might/can be, if they bother, which they probably will), maybe that stuff will be option though.).
And er, does it have to be Ubuntu? I suppose it does actually, seeing as if we want CDs en masse we could get them off cannonical. SuSE (only OpenSuSE?) might be another option (could ask Novell), and it's supposed to be good too.