There was a topic about this a month or so ago..
With TrueCrypt you can encrypt the whole drive or portions of it, sure. I really only wanted to encrypt my source code too, like yourself.. and was a little bit worried I'd kill performance if I encrypted the whole drive. But I use hibernate a lot and learned that source code would also be readable in the hibernation file if I didn't encrypt it and someone got hold of my laptop, so had to use full-system encryption anyway.
Been running that for a year now, and not looking back. Just make sure you got AES-NI instruction support and you're golden! I actually got a small boost in performance over running no encryption. Look up the other thread if you're interested in why.