need password advice w2kAS

Hello: We have a w2KAS file/web/print server for our small business. I want to access a data file which is located on one of the PCs, but use the app to manage the data from another PC. All the PCs are seen by all the PCs - that is, their icons are in each PC's network neighborhood. (I've enabled sharing for the drive holding the data.) But I cannot seem to actually log on. The 2 PCs in question are both w7pro. All PCs can access the server w/o problem. But for security reasons that data file must stay where it is, so the regular user must leave when I need to work on that data.
-All are in the same domain (whose name appears on each PC); all on same subnet.
-Will a W2K server allow any file sharing between 2 w7 PCs?
-Where is the password verification occuring - on the server? on each PC ? Both PCs & server?
-where do I find/change change the permissions/enter passwords? ALL the places, please. (I thought I knew, but obviously nothing I've tried yet has worked.) Is the password for server access different to get thru to the PC's files, so I need a password stored on the host from the client, which is also separate from that of each PC to access the server? So also, while I've worked with active directory, it's not enough, nor with the twists & turns of w7.

Useful w7/w2K c/s sites/tutorials welcomed too, that have answers.
Thank you.