Network / Sharing :: How To Declare Locations As (inside Your Local Network)

I have an old computer that I've repurposed as a file server for all the other machines on my network, and one of the things I do with it is to put various program installer files on it, so I can install them to the other machines without having to download the same file over and over. However, when accessing these remote files from any machine except those still running XP, I get an extra warning box telling me that the file "is in a location outside your local network." It's not, but for some reason, these machines think it is. I've Googled various fragments of text from these warning boxes (each Windows version has slightly different wording for this warning; the screen shot I've attached is from the Win7 machine I happen to be on right now), but no matter which variant I search for, everything I find about getting rid of this warning is either geared toward similar warnings given by MS Access for remote databases, or for marking external Web sites as trusted.

How do I tell Windows that this local file server is in fact local and not in need of these repetitive and annoying warnings?