All of the sudden I cannot type " \\my.server.ip.address" in explorer to access shared files/folders like I used to. I could have possibly changed GPO or RDP-TCP settings to screw this up, but I don't remember, and nothing looks odd or different. What is this called and how do I fix it? Host is Windows Server 2003 running terminal services; clients are XP workstations, all on the same domain, and I have no problems connecting via RDP.
I'm not sure if it's a typo, or the solution to your problem... but:
Should have two slashes, like:
Does it work by name, and just not by IP?
Not sure I'm understanding but if the problem is "none of the XP clients can connect to the 2003 machine share", try restarting the Server Service on your 2k3 box (services.msc). It will say some other things depend on it, that's fine - allow it to restart those as well.
If that doesn't work, and the obvious reboot technique doesn't work either, then try the following which has worked for me in the past on Windows XP (and by extension should work on 2003 as they share a lot of code.)
Go to the network control panel, remove Client For Microsoft Networks by unchecking it. Then re-install it. This re-installs the workstation (server service too?) and will usually jolt the MS core networking (shares, network neighborhood) back into place.