It look like both the TX and TZ range are ultra light laptops for people on the move.
Note they only have 11" screens which are VERY small so make sure you know what you are buying.
The TX range has Intel U1400 & U1500 processors
The TZ range have a U7500 & U760 processors which are better (core duo).
The TZ seems to be part of the "style" range so you are paying a lot for the fancy styling. They cost between �1500 and �1900.
So after a quick look I would say the TZ are the better of the two, but as I said, you are paying a LOT of money for a very small lightweight laptop.
More on processors
http://www.intel.com/products/centrino/compare .htm
TZ with prices
http://vaio.sony.co.uk/view/ShowProductCategor y.action?site=voe_en_GB_cons&pageType=Models&c ategory=VN+TZ+Series