Is there a way to encrypt an entire partition with existing files still stored on it?

I have an external drive I would like encrypt. When I create a new volume in TrueCrypt and select the drive's partition, it only gives me the option to format the partition first and then it will encrypt it - causes all the data to be erased. Is there a way to encrypt an already existing partition without moving all the data somewhere else?

Truecrypt is a volume encryption method, not a file encryption method, so you have to start with an encrypted volume. However it's well worth the extra work, (saving the files somewhere else then moving them back) for two reasons:

1) Plausible deniability. The drive has a huge area of random data on it - there's no way to tell that it's encrypted files.

2) Using triple encryption, the person who can break the encryption's grandparents haven't been born yet.

I am not sure if this will help, but I use File Barricader for all of my encryption/decryption needs. It can encrypt any files you want, and there is no reason why it wouldn't be able to encrypt the entire HD, except that it might take a while.

It's free, and very easy to use. Give it a try and see if it helps.

I'm using Pointsec encryption, it also handles the data in place.