The Proworx32 user interface is quite a bit different than NXT - and not for the better. 32 is a dog, its slow and sometimes seems to hang for several seconds, although it hasn't totally crashed on us. We have the latest version and many of the bugs of earlier versions have been fixed, but so far I'm not impressed with it. However, we had difficulties running NXT under XP SP2, though it seemed fine under XP before SP2. I have heard of people running NXT on a VM, although we didn't have much luck with that.
We also have FasTrack Sofwork's PLC Workshop 32 for Modicon. Its faster and easier to use than Proworx and I would be happy with it if it wasn't for the frequent blue screens (on two different computers).
Right now there simply is not a software package that I can recommend for Modicon 984LL.