I installed 4.2 on my iPhone 4 and installed the iTunes 10.1 beta (64bit) on my Windows 7 PC. When I go to print from the iPhone it does see my HP LaserJet Printer I have connected to my Windows 7 PC but there is a lock on it. It prompts me for a password but I can't figure out what login/password it wants?
UPDATE: Ah. I did a Google search and found this...
"On a PC, iTunes 10.1 is necessary to use AirPrint. On a Mac, support for AirPrint is built in to the forthcoming Mac OS X 10.6.5 build of Snow Leopard.
PC users on Windows 7 will also need to enable a "Guest" account on their machine in order to use AirPrint. Without it, an iOS device asks for a username and password, and cannot wirelessly print through Windows."
After I created a Guest account I was able to send a few pages to the printer successfully. However, it seems a bit flaky at times and sending a page seems to take a number of minutes (a lot longer than I would expect). But it works. Not something I would use often but pretty handy if I come across a page that I want a hard copy of.