Hi Leslie

Bootcamp comes for free with every Mac. Kind of like the toy in a Happy Meal. You do need to have a copy of Windows on CD though, so you might have to purchase that. With your copy of Windows at hand, launch Applications/Utilities/Boot Camp Assistant on your Mac and it will walk you through the installation. There's lots of help on this on the 'net, just google it if you need to.

Once Windows is installed, you should be able to download and install the latest version of DirectRT.

Whether the MacBook Air is mighty enough for your task depends on what you want DirectRT to do. The answer is "probably yes". The timing may not be that good if you run off battery; best if you have it plugged in when running. We've done ERP and fMRI studies (where timing is important) in DirectRT on a ca. 2006 MacBook Pro, which is probably roughly equivalent in performance to a current MacBook Air.