Went downstairs on my xp laptop (15.4" seems adbsurdly huge after using my 9 for a month!) and think I have it figured out:
In the "Wireless Network Connection" window, the one where you select which wireless network you wish to join, look on the left side of the window for a sidebar titled 'Network Tasks.' The second item in this taskbar should be called 'Set up a wireless network for a home or small office.' Click that, and go through the wizard to create an ad-hoc network. Good luck!
One additional note: Windows allows you to share folders/drives over whatever network you're a part of. I don't know if you have specific circumstances that necessitate an ad-hoc network, but if all you need is folder sharing, that can be accomplished if both computers are connected to your regular centralized home network, circumventing the need for creating an additional ad-hoc network. You can't, however, simply use a networked optical drive the same way you would use a built in optical drive, regardless of whether you're using a centralized or ad-hoc network. You can access any files on the optical media, but if the application you're using needs to verify that the cd is in the tray, verification will fail b/c the drive isn't actually local.
Hope all this helps!