I wanted to have an ultrabase with a dvd-rw drive for my new to me x61t- I purchased one on Ebay, but it turned out to be the wrong one, and the ultrabase that is compatible with the x61t is hard to find.

Now I have the base and a removable dvd-rw drive - Is there an external dvd-rw drive box that I can use with my drive? I have read that there are sometimes compatibility issues. What kind of drive housing would you recommend I get to go with my existing thinkpad drive? Thanks in advance for your help.

I bought a cheap USB2.0 case like this: http://www.ebay.com/itm/USB-2-0-Externa ... 0885105496 and put in an old 12.5mm thick DVD-ROM I had lying around.
Your drive is Ultrabay Enhanced, so should have the same dimensions and fit in this USB case.

Thanks for your answer to my question. To clarify, I just need to get the housing , and my thinkpad dvd-rw drive will fit right in? I don't need anything else? Thanks so much.

Yes, that's all.

Almost! That enclosure is for a "standard" drive, which means you need to detach the Lenovo-specific connector/mapper from the back of the drive, i.e., take the drive back to its non-Lenovo virgin state. If you want to use the Lenovo drive unaltered, you need the following or something similar:
http://www.ebay.com/itm/Slim-DVD-CD-Ext ... 2eb9d60312

Which of the 2 above is better? I am a little unclear on how they are both different? What are their Pros & Cons?

If you want to take a drive out of a Thinkpad and place it in an external enclosure, without doing anything to it, then the one I referenced is "better". If you want to place a drive which does NOT have the Lenovo-specific add-on connector (which is pre-attached "permanently" to Lenovo drives, but which can be removed, but not intended to be removed!) then the first adapter above is "better".

The connectors on these drives are "standard", but most laptop manufacturers, including Lenovo, use a proprietary connector, and they attach a small mapping connector/cable to the drive so that the drive mates with their proprietary connector. The proprietary connector appears attached "permanently" to the drive, and to remove that connector sometimes one needs to undo tape and screws which were not meant to be undone. Such is the case with Lenovo's drives, also. The two enclosures above accept either the "virgin" drive's connector or the Lenovo-specific connector on Lenovo's drives.

Hi the X6 Ultrabases look so similiar I was wondering what makes the non Tablet incompatbile with the Tablets?

Geometry, i.e., the position of the connector, registration slots on bottom of machine, etc.