hi,
try to search on M$ KNOWLEDGE BASE : ID Q135818
u may also use Win32api

I got the sample as th following:
DECLARE INTEGER GetLogicalDriveStrings IN Win32API as getit;
INTEGER nBuffSize, STRING lpString
CLEAR
DIMENSION aMyarray(1)
lpString=SPACE(200)
nBuffSize=LEN(lpString)
=getit(nBuffSize,@lpString)
NumberOfDrives=OCCURS(":",lpString)
DIMENSION aMyarray(NumberOfDrives)
FOR i=1 TO NumberOfDrives
aMyarray(i)=SUBSTR(lpString,AT(":",lpString,i)-1,1)
ENDFOR