in VFP5.0a I use
PUBLIC lpUserIDBuffer, ;
nBufferSize, ;
RetVal

RetVal = 0
lpUserIDBuffer = SPACE(25) && Return buffer for user ID string
nBufferSize = 25 && Size of user ID return buffer

DECLARE INTEGER GetUserName IN Win32API AS GetName ;
STRING @lpUserIDBuffer, ;
INTEGER @nBufferSize

RetVal=GetName(@lpUserIDBuffer, @nBufferSize)
lpUserIDBuffer=subs(lpUserIDBuffer,1,len(alltrim(lpUserIDBuffer))-1)
? lpUserIDBuffer
return lpUserIDBuffer