Don't know if I'd say I'm an expert...I've just tinkered around with NAV and NIS quite a lot.

But as far as virus definitions go, I've never had luck with putting newer virus definitions in the install source VirusDefs folder. If you want the most up-to-date definitions when you install your Norton product, compress the folder found at C:\Program Files\Common Files\Symantec Shared\VirusDefs, and make a SFX file that extracts the folder back to that location prior to installing the program. (Of course, before you make the SFX, delete all but the most recent virus defs folder - for instance, if the first three folders in your computer are named 20050122.012, 20050123.001, and 20050124.012, the most recent ones are in the last folder (20050124 = date the defs were released; .0xx=version of the defs made on that day).)
You should be able to make a SFX RAR of the NAV 2005 install source that is 22.0 MB compressed. Adding the virus def SFX adds about 5 MB, and your symlcrst.dll SFX should only be another 200 KB on top of that.