You should use Best Crypt ( that is what I use ) or True Crypt both are good. You just need to purchase it or try finding a license for the software and install it. Then you will need to encrypt your hdd which will take a few hours, depending on your size. I also advice you to install some erase programs like Secure Clean or Evidence Eliminator, both are good.
In order to be fully annonymous you should also purchase a VPN that will ensure that your traffic is securely encrypted.
As for instant messaging programs just install Pidgin with the add-on OTR.