The HGT 1.9 multijet was introduced with the 'Mk2.5' Punto and has been on sale for as long as the rest of the range.
It is indeed a 100bhp engine with 8 valves, not 16. The performance stats posted by the negotiator are indeed correct.
The difference between multijet and JTD is that JTD uses a single high-pressure jet (1600 bar?) for the combustion process where as the multijet uses a number of lower pressure jets for each combustion explosion. The advantages of this are fuel is burned much more efficiently (you get more performance from the same 'bang' on each cylinder because the single 'bang' leaves unburned fuel, hence the black smoke coming out the back of diesel when the engine is 'on-load') and the technology tends to be quieter (rather than 1 big bang, there are a number of smaller ones).
If you live life on the rev-limiter the 1.8 HGT is the way to go, but if you drive like a normal person and prefer torque to pull you around, the JTD is unbeatable. In the real world, turbo diesel is much faster
Oh, and if you buy the 1.8 you will struggle to get 30mpg (especially if you use the performance) but the multijet should get 50mpg regardless of how hard you drive it
The 85bhp 1.9JTD is still on-sale in the 'Mk 2.5' Eleganza specification only. For the new Punto this engine will be replaced with an uprated version of the 1.3 multijet engine. Power will go up to 90bhp, and torque will rise to about 160lb/ft @ 1750rpm. This engine was supposed to come with 'Mk 2.5' but has not been fully tested. Don't ask me how I know, I just do