I am using TrueCrypt's 'Full Disk Encryption' and according to TrueCrypt's FAQ I should 'Permanently Decrypt System Partition/Drive' before reinstalling Windows. This does not make any sense to me. Would reinstalling Windows not undo the encryption in the first place?
The reason I would like to know, is because 'Permanently Decrypt System Partition/Drive' will take a long time.
Note: If the system partition/drive is encrypted and you want to reinstall or upgrade Windows, you need to decrypt it first (select System > Permanently Decrypt System Partition/Drive). However, a running operating system can be updated (security patches, service packs, etc.) without any problems even when the system partition/drive is encrypted.