So you've decided you need more security for your saved bank statements, you need to encrypt an entire harddrive, you don't want anyone viewing your personal files, if any of this sounds familiar your in the right place.  TrueCrypt is the only open source on the fly encryption that I know of that works this well.  You can encrypt what you need to, you can encrypt whole harddrives or operating systems you name it you can encrypt it.  If you don't have anything other than a windows password for security you should be looking at this app for sure.

From TrueCrypt :  Creates a virtual encrypted disk within a file and mounts it as a real disk. Encrypts an entire partition or storage device such as USB flash drive or hard drive. Encrypts a partition or drive where Windows is installed (pre-boot authentication). Encryption is automatic, real-time (on-the-fly) and transparent. Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted. Provides plausible deniability, in case an adversary forces you to reveal the password: Hidden volume (steganography) and hidden operating system. Click the Blue Arrow below to download.