There's a fun little test app (with source) called IPCWorkshop at http://www.codeproject.com/threads/ipcworkshop.asp
I noticed it probably needs a Sleep(500) in its Mailslot receive loop, and a lot of its stuff doesn't seem to work on my Windows Me system, but its "filemapping" and "mailslots" modes do seem to work on Windows Me. (Oddly, "Clipboard" doesn't work for me on Windows Me. This app is fairly new, maybe it's still a bit buggy.)
None of its modes seem to work on Wine. Not sure why. In server mode, it never redraws, so the GUI is messed up somehow. I'm sure this app triggers several Wine bugs.
Anyway, if anyone's looking for simple test apps that exercise various IPC methods, this one might be worth checking out. - Dan