Hello:
The M6600 is constructed very similar to my M4600. As a matter of fact, they even use the same manual. The "Primary HDD" cage does indeed pop or "eject" out very easily by removing the battery to get to the latch.
http://support.dell.com/support/edocs/systems/wsM6600/
You can review the product manual online and see how to remove the primary HDD. There is 1 single screw under the battery (remove the battery) that holds the "release latch" in place. Remove that 1 screw and put it in the original box for safe keeping. Then, all you have to do is:
1) Remove battery.
2) Slide the latch.
And the HDD just pops out the side. The HDD caddy uses no screws, so you can quickly swap HDD/SSDs. I use this for when I am travelling, and don't want my laptop subject to unwarranted searches. My internal mSATA PCI-E card in the laptop holds a bare-bone install with no browser history or files, in case they do search it.
