Thats entirely up to Uncle Bill I'm afraid!! Have queried this one myself on various forums...Our Bill's company is a monopolistic setup and its all down to the men in suits as to when they take this step.It certainly wont be a while yet...I was offered the test version as part of a Microsoft feedback programme and ran Vista on a Dual boot system..Some impressive improvements but I'm staying with XP and Firefox for now !!!
I disagree with fo3nix (but have nothing to back it up)
I DONT think XP will be available on CDs for a few more years.
The Retail (boxed) and OEM versions will probably not be availabe for very long after Vista comes out. Probably until stocks run out.
For enterprise customers, who have a large existing user base on XP, they will still be able to purchase and install the enterprise version of XP on new PCs.
You'd be surprised how much longer the OEM stuff still sells for; either demand or simpler surplus stock everywhere, I'm not sure. You could still buy win2k up to a few months ago.
Having said that, the 'at least a few years more' comment I made does seem far wrong. Maybe a year I'd think, or two.