Can’t map to/ping machine on the network

We’re a small office running several Windows servers with XP on the client. We run virus software on our network by mapping to the c$, d$ and so on drives on the clients, then run the software on a dedicated server.

There are some machines that I can’t map to or even ping. I’m a domain admin.

It seems to be caused by having the Windows Firewall turned on. But turning that off scares me a bit as well. Is there a way to map to a drive (admin share or otherwise) and still have the Windows Firewall turned on?