This may help. It's some code I got from Russell Campbell on the MS newsgroup a few days ago and it finds the UNC from a mapped drive:

MyFileName = "F:\APPS\WORD\WINWORD.EXE" && Replace with a file name on your
network drive.
DECLARE INTEGER WNetGetConnection IN win32api ;
STRING lpszLocalName,;
STRING lpszRemoteName,;
INTEGER @ lpchBuffer;
API function
slpRemoteName = SPACE(254)
slen = LEN(slpRemoteName)
iSuccess = WNetGetConnection(left(MyFileName, 2), @slpRemoteName, @slen)
IF iSuccess = 0
? MyFileName + " = " + LEFT(slpRemoteName, ATC(chr(0), slpRemoteName) -
1) + substr(MyFileName, 3)
ENDIF