I've had this exact problem. I contacted the Kittyhawk 737 designers to find out why their 737 models are invisible in FS2002 whereas their previous FFX versions weren't, and it's because the Kittyhawk models are exported from GMAX using the FS9 MakeMDL utility. This isn't compatible with FS2002 so you don't see the model.
The initial release of the PSW CRJ-700 (Air Dolomiti colours) must have been exported using the FS2002 MakeMDL because I can see it in FS2002. However I haven't downloaded the updated Beta version but it may well be that the new version was exported using the FS9 MakeMDL utility.
I don't think there's anything we poor FS2002 users can do about this, apart from beg the designers to go back to using the FS2002 MakeMDL. The resulting planes are I think visible in FS2002 and FS9. (Anybody know different?)
