Windows 7 startup repair with Truecrypt

http://www.truecrypt.org/docs/rescue-disk

If Windows is damaged and cannot start, [...]

Note: Alternatively, if Windows is damaged (cannot start) and you need to repair it (or access files on it), you can avoid decrypting the system partition/drive by following these steps: Boot another operating system, run TrueCrypt, click Select Device, select the affected system partition, select System > Mount Without Pre-Boot Authentication, enter your pre-boot-authentication password and click OK. The partition will be mounted as a regular TrueCrypt volume (data will be on-the-fly decrypted/encrypted in RAM on access, as usual).

If you're quick enough, you can hit the [F8] button immediately after pressing Enter (after entering your TrueCrypt password) and it will give you the ability to repair your computer or enter any of the safe modes, etc.

Just verified it using Windows 7 Professional and TrueCrypt 7.1.

You can partition the 500gb disk to 50gb system partition or something like that, then you just have to decrypt 50gb(only the system disk/partition).