Is this a high vacuum application?
If so then I use convectron gages from Granville Phillips for ATM down to 10-3 Torr and ION gages for 10-4 down thru 10-7 Torr.
These gages have a logarithmic 1/decade ouput. If you need it I have a linearization routine for them.
If this is a lower vacuum applicaton such as you typically find in material handling, where pressure is measured in inHg rather than milliTorr then an absolute pressure transducer is more what you are looking for.
---edit
Nevermind, I see you posted while I was typing and you are measuring in inHg.
The 4-20mA input can be converted to 2-10V by placing a 500 ohm resistor across the input (ohms law: 10V = .020amps * 500ohms). Use an SCP instruction to scale the value to account for the 2V "live zero." The ML1100 built in analog input is a 10 bit input. That means that you will be able to resolve one part of 1024. Probably good enough for vacumm that is measured in inHg,