Mac osX on WinXP/98 Net

Hello.
I will admit that I am a network dabbler. Most (all?) of what I know about networking, I have found out through trial and error. Which is why I am posting presently.
I have a network that I manage at my family's printing business and have it setup to share several printers that are all connected to a router. Though it has been frustrating at times, I managed to get them all setup so that all the computers are able to print to every printer on the network. They can also all access the internet independently of each other. What I would like to do now, is enable each of the computers to see/access files on any other computer without having to cart USB drives/ cds / floppies(gasp) back and forth.

Here are the details of my current configuration:
Computers:
2 - WinXPsp2
1 - Win98se
1 - Mac OSX (not sure which version offhand)

Router:
CompUSA 8-port DSL Gateway (connected to one of AT&Ts DSL modems for internet access, not sure of it's model)

Hub:
4 port LinkSys 100

Printers/Copiers:
Minolta di550
Minolta 8031 color
Xante Platemaker 3 (2 of these)
Xante CL30 Color Printer (also 2)
Brother 1850 (connected to the Win98 via parallel)

Other than the Brother printer, each device is connected via cat5 cable to either a hub or the dsl gateway. We do not have any wireless needs/capabilities at this time. Most of the printers each have a network controller onboard that have various web interfaces for setting them up (except the brother). The network is all setup using a peer-to-peer arrangement. As far as I know, the only protocol I am using at present is TCP/IP. The Windows computers more or less talk to each other (tho I do have some trouble accessing the 98 from the XPs, particularly deleting files). All 3 windows comps have ZoneAlarm AV running on them and Windows firewall(fireVent, more like) turned off. At present, I don't have any 3rd party firewall/AV software running on the Mac. I am not very familiar with Mac, but I think it has an inherent firewall in OSX, which is likely running (don't know anything about it).

The sheer volume of material that is available regarding networking, has kept me unwilling to try to sort through it all to find pertinent information to my needs. And as I don't presently have the desire/time to pursue a networking technician's degree, I'm unable to determine what classes (if any) at my local community college might help. So if anyone has any suggested reading/websites/tools/classes that would help me understand how to better manage these systems, I would greatly appreciate your responses.

Sorry about the length. Thanks in advance for any help,

Shawn K
network dabbler