I'm not sure the TrueCrypt solution will work. Normally when you create a filesystem/partition, the tools write out the minimum data they can - generally the partition layout in the MBR and the file allocation table at the beginning of the disk (and in a number of backup places throughout the disk in the case of ext3/ReiserFS/any decent modern filesystem). Formatting your drive rarely overwrites all of the data on the drive, it just leaves the file data intact and marks those regions as 'unallocated' so that the system doesn't get confused.
TrueCrypt /might/ overwrite the whole drive, but I certainly wouldn't take it for granted - it's intended to protect the data contained within the new filesystem, not the data that was there beforehand. Generally you can tell by how long it takes to format the drive - assuming a sustained average write speed of 150MB/s it would take almost 4 hours to fully overwrite a 2TB drive - with encryption this is likely to take even longer.
You could of course create the TrueCrypt partition and then fill it up 100% with whatever data you want, e.g. dd if=/dev/zero of=/mnt/truecrype/file, but this would still leave one piece of data on the drive - your TrueCrypt password - so be sure to set this to something you don't use for anything else ;)
I doubt anyone has the resources to use an electron microscope to partially recover some of the data from your drive for teh lulz, so unless you have something serious to hide I'd suggest that just overwriting the drive with zeros using dd is perfectly sufficient - this should erase the MBR and partition layout too, not just the data on the partitions. If I was really worried then I would then smash the drive with a lump hammer to necessitate physical recovery. You are talking about a semi-modern HDD - not a 256MB one - right?
Cheers,
Benjie.
PS: A quick glance at the TrueCrypt 'beginners tutorial' has this note (relating to creating a filesystem in a file):
IMPORTANT: Note that TrueCrypt will not encrypt any existing files (when creating a TrueCrypt file container). If you select an existing file in this step, it will be overwritten and replaced by the newly created volume (so the overwritten file will be lost, not encrypted). You will be able to encrypt existing files (later on) by moving them to the TrueCrypt volume that we are creating now.*
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