There is a howto in the beta section of the old forums: BT4 Encrypted HDD install using LUKS and LVM - Remote Exploit Forums there.
I don't recall seeing a luks option last time I installed BT4F, but it could well have been there. Luks is about the best option available to us Linux users (in general).
There is also Truecrypt, but so far I've found it a bit hit and miss, so I don't tend to mention it much.
This is all rather useless (LESS I SAID, NOT USEFUL! Stupid mind getting ahead of me) though - you can do cold boot attacks to get the encryption keys (Hak5 did a video on this IIRC), and you can also just install a hardware key logger to snarf the keys from the user anyway.
You can go really paranoid if you want to and start CD booting your machines and hardware encrypting them etc. I make use of thermite (and have done so longer than Knuth has been in those books ) and other things when I want to be sure my data is safe, but it makes it a little hard to get it back.
And occasionally I forget and open the wrong server casing... it's not fun to have to keep your entire closet from catching alight