Accessing PC on network

While the Macs can see each other, they cannot see the PC nor can it see them

There are so many ways that could work (or not, as the case may be), it would be difficult to list them all. The short answer requires more information about your network setup. Posting the IP addresses of each machine would help - at least it would tell if all the machines are in the same subnet, which is going to be the easiest way to make it work.
If you don't feel comfortable posting the IP addresses here (although if you're on a private network it won't matter), check each machine to make sure that all the IP addresses are in the same range - that typically means that the first three numbers match (e.g. 192.168.1.x).

I know I should enable file sharing, but HOW???

On the Mac, System Preferences -> Sharing -> WIndows File Sharing

File sharing on Mac as you suggested. What about the PC?

I have no idea, sorry. I don't do Windows.

Go to My computer > My Network Places > Set up a home or small office network

The wizard will guide you through the set up process which is fairly straightforward

You will need to allocate a folder for sharing - the macs should log on to this when you connect

Once that is done (and after a few re-boots of computers, modems & routers) the PC should appear in the Network globe in finder on the Macs

To find the Macs on the PC, go to View Workgroup Computers

All of this assumes that all your computers are set to obtain IP addresses automatically

http://www.ifelix.co.uk/tech/3020.html

Be sure that the macs and PC have the same workgroup name in the appropriate places.
(mac, this is found in Directory Access>SMB configuration)
(PC, it's in System Properties, ComputerName....)