Belkin have a USB to parallel adapter..
http://catalog.belkin.com/IWCatProductPage.process?Merchant_Id=1&Product_Id=20651
Generic models (eg. EBUYER own brand) can be considerably cheaper - or you can also find one ($10 more at Belkin) which provides a full set of ports (Parallel, KB, Mouse, Serial and a USB hub as well).
The port uses it's own drivers, and most Printers should be able to work through any Windows-supported port.
Not seen a 1:2 switch at Belkin, only the other way round - 2 computers to one printer, though 2:2 crossover switches are around, and could probably be used as a 1:2
For a print server, you would have to network it to (say) an old desktop, serving the printer(s) connected to it - you can get broadband routers which combine a network print server, or standalone Ethernet print servers with 1 or 2 parallel ports.
Chepest option would be a manual switch, though I seem to recall some objection to "live" switching.