CarolynnP..
I recently bought a 2011 Macbook Air 11" with 256GB drive and the latest Mountain Lion to use as a Windows PC while travelling. I already have a 15" Macbook Pro at home for producing music and I need quite a few Windows-only apps for my work as a software developer, so I decided to install Windows 7 on the Air and remove OSX completely.
You will need a Windows 7 installation DVD, an external USB DVD drive (one from a PC should work), and a USB external hard-drive of sufficient capacity to back up the entire hard-drive of your Mac - those are quite cheap from Maplin, Frys, Wal*Mart, Dick Smiths etc. depending on where you live.
1. Download a Mac program called "Carbon Copy Cloner" and make an exact copy of your Mac's hard drive to the external USB drive. After copying, check that you can boot from the copy by pressing & holding "Alt" immediately after switching on your Mac.
2. Go into Bootcamp Assistant and download the Bootcamp drivers for Windows. Save these to a thumb-drive. This takes a while as it's a 700MB download!
3. Connect the external DVD drive and insert a Windows 7 install DVD. Reboot the Mac and press+hold Alt immediately after switching on. When the boot options appear, select the DVD.
4. Delete all Mac partitions and load Windows as normal.
5. Once windows starts, insert the thumb-drive containing the Bootcamp drivers and load them. You should now have a fully-functioning, small, light & trendy Windows 7 PC.
I've read a lot about how battery life is impacted by running Windows under Bootcamp on a Mac. I've been using this for 2 months now and I'm getting 6 to 6½ hours on a full charge, which is about the same as under OS X. Presumably because Windows 7 supports UEFI natively, the BIOS doesn't have to be emulated, saving power. The trackpad, screen controls, keyboard backlight etc. all work perfectly and even sleep/instant-on works when the lid is closed.
Another problem folks often cite regarding removing OS X completely is that if the UEFI needs updating (or power-on brightness changed etc.), this can only be done under OS X. This is what the backup is for. Any time you need to go into OS X, plug in the external drive before starting-up and press+hold Alt to select the drive. You can get into OS X any time to do updates.
Hope this helps..
Gordon