I have 21.5GB free. Why won't my MacBook Air 2010 let me use Boot Camp? I'm trying to install Windows 7 on my MBA, 2010. 

I open up Boot Camp and attempt to use it, but after the first screen it comes up with an error saying it can't install unless theirs 10GB of free disk space. Right now my HDD has 21.5 GB free. Disk Utility won't let me partition my drive either, so a manual install is out of the question.

I need help! My original thoughts were that my disk needed to be defragged to get 10GB of contiguous space. Is this a possibility?
To expand upon my above comment:

64GB is just not very much space, especially when you consider updates, your own programs, data, etc etc.

My recommendation, if it is possible and available, is to run Windows XP from a USB drive. There are a handful of documented procedures for getting WinXP on a flash drive and running it from there. I would recommend following this TechRepublic article to get it all set up for that.

This should negate the issue with Boot Camp, let you keep the 64GB of HDD space to your trusty OS X partition, and hopefully provide enough room on your flash drive for WinXP to grow with applications as well. 

Hopefully there is nothing Vista or Win 7 specific that you need to do. Good luck!