I believe you can use 1 ts for 1 cs not 1 for 2 ? ( can anyone confirm) however it wouldn't be the best use of your TS credit and may mean you don't save money on the plan.
Have you checked the (very well-maintained) 2007 Dining Plan FAQ 'sticky'? http://disboards.com/showthread.php?t=1305783
"Can I use TS credits for CS meals?
No. During the last free dining promotion, Disney did extend an offer to use TS credits for CS meals (plus two snacks and a cheap lanyard), but that offer has expired. Prior to that offer, some (but not all) hotel front desks allowed some (but not all) guests to convert some of their remaining TS credits in the CS credits, with the understanding that once converted they cannot be converted back. However, that is not an official part of the Dining Plan, and so you may or may not be successful in getting them to do that for you."
It should be noted, the Disney Dining Plan does not work for everyone. If a Guest prefers not to spend time at table service restaurants on a daily or almost-daily basis, most likely the DDP will not be cost- or time-effective for that Guest.