I'm in the boat of needing a 4x4 with a diesel. I'm currenty pretty set on a ram with a cummins, due to lack of choices. It's a bit bigger than I need/want, but I believe the liberty will be too small, and the Touareg too expensive.
The Touareg has already been released with the badboy TDI engine in Europe, and is rumored to make it over here to the states at some point. It's a V10 TDI engine, making some 330hp and 500lbs of torque. Similar to cummins power but in a much smaller vehicle. Supposedly it does 0-60 in under 7 seconds. Only downside is that it will be around $55k. Repairs may be expensive as well, imagine replacing 10 glowplugs!!
The liberty will be available late summer '04 as an '05 model with the 2. 8L commonrail injection 4cyl diesel. The engine is built by VM Motori in Italy, and the Liberty diesel has been out on the roads in the UK with this config for 2 years now. This will hopefully avoid the new bug syndrome(cough cough ford 6. blow). My thoughts are it's just too dinky and small. There is virtually no trunk space.
Excursions are way too big and slow and ugly for me. Therefore the only choice(since I MUST get diesel

) is the Cummins ram. Too bad those Touaregs will be so expensive. I'm excited about the beast though. I'm thinking of picking up a black 03 laramie in a week or two.
Another interesting diesel 4x4 that may come out soon, is the Crosslander. It's powered by a 2. 8L Powerstroke diesel and an Eaton transmission. It's way rugged, basic , and offroady. Options include air intake snorkel, winches, roof racks, light bars, etc.
www.crosslander4x4.com
Here's a pic of one.
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