Try using java.io.File. Read the api for the applicable
disclaimers.
http://java.sun.com/javase/6/docs/api/java/io/File.html#getFreeSpace()
<cfset f = createObject("java",
"java.io.File").init(pathToVolume)>
<cfset free = f.getFreeSpace() >
<cfset total = f.getTotalSpace() >
<!--- function found at:
http://cflib.org/udf/ByteConvert
--->
<cfoutput>
total = #byteConvert(total, "MB")#
free = #byteConvert(free, "MB")#
</cfoutput>