Here you are Sir. I was able to get set up the HP 5850 (which I just recieved yesterday and opened tonight espicially for you) to connect in Ad-hoc mode. It was very easy to do. Here is what I did.
1. Opened box and read instructions (always helpfull)
2. Plugged in printer, inserted paper, and ink cartridges.
3. Read manual, and found out to set up ad-hoc, you need to hold down the network and then press the resume button, while still holding down the network button. Release the rume button first, then the network button. Press netwrok button again and a networking page prints out. ( The networking page doesn't really tell you much, other than that the print is in ad-hoc mode now, and the SSID, which is HPSETUP, as if you couldn't tell that was the printer)
4. Went to my airport signal thin in the menu bar, and selected HPSETUP.
5. Opened Printer Set up utillity and selected Rendez-Vous. Then clicked on add printer. It searched for a second, then it found the 5850. Clicked OK.
6. Printed a test page. Every thing works great. No need to install any CD software or anything. Although I think it would be best to secure the ad-hock network. I assume anyone within the area could technically print on the printer right now. (Goes and turns off printer)
So thats basically it. If you have any questions feel free to ask, ill do my best to answer them. Also Bestbuy.com has this thing for 199.99 +plus tax and free shipping. CompUSSR has it for 179.99 last time I checked. I purchased it from Best Buy as I can easily return it without any restocking fees if I change my mind. Might be something to consider. Good luck with you new printer. I like mine alot.