TrueCrypt is the tool of choice to encrypt your computer hard drives, and under windows it offers the option to encrypt the system drive on the fly, which is very comfortable. As you might guess, this could also go terribly wrong, which is why TrueCrypt forces you to create a rescue disk ISO, which has saved me a lot of trouble in the past. However, by default, TrueCrypt does not let you encrypt your system drive before you have actually burned that image to a real CD, and that, on the other hand, is quite annoying in a day and age where many notebooks no longer have an optical drive. What few people know - this check can be turned off by executing
If you don't believe me, try it yourself or check out their documentation.
"TrueCrypt Format.exe" /noisocheck