The new midsize sedan is definitely NOT going to be released as a 2010 model. My best guess is 2011. The Jetta will be a separate model from the Golf (in the past they were the same car except for the hatchback vs. trunk). The car will be slightly bigger than the current Jetta. Since no official details have been released, anything more is pure speculation. Worst case scenario, VW decides to not certify a TDI engine in the new body for a few years. They did it with the Passat TDI - there was a 1996, 97 and then no more until 2004!
If I were you, I'd get a 2010 Jetta or Golf TDI. The Golf TDI has an all new body and it's getting very good reviews. The 2010 Jetta sedan is mostly carryover with some minor changes like bluetooth and a new radio. The 2010 Jetta wagon is getting major cosmetic changes and a number of significant changes but rides on the older body.
The reason why is because there are a number of tax incentives available right now for 2010 on new cars, see these pages for more details on the 2010 and tax incentives:
http://www.myturbodiesel.com/1000q_how_to/a5/09_10_TDIdifferences.htm
and
http://www.myturbodiesel.com/1000q/TDItaxcredit.htm
If I were you, I'd get a 2010 Jetta or Golf TDI. The Golf TDI has an all new body and it's getting very good reviews. The 2010 Jetta sedan is mostly carryover with some minor changes like bluetooth and a new radio. The 2010 Jetta wagon is getting major cosmetic changes and a number of significant changes but rides on the older body.
The reason why is because there are a number of tax incentives available right now for 2010 on new cars, see these pages for more details on the 2010 and tax incentives:
http://www.myturbodiesel.com/1000q_how_to/a5/09_10_TDIdifferences.htm
and
http://www.myturbodiesel.com/1000q/TDItaxcredit.htm