Set DiskSet = GetObject("winmgmts:{impersonationLevel=impersonate}").ExecQuery("select FreeSpace,Size,Name from Win32_LogicalDisk where DriveType=3")
for each Disk in DiskSet
If (Disk.FreeSpace/Disk.Size) < 0.30 Then 
WScript.Echo "Drive " + Disk.Name + " is low on space."
End If
Next

create table ##diskspace (details varchar(1000))
insert into ##diskspace
exec xp_cmdshell 'cscript c:\disk.vbs'

if (select count(*) from ##diskspace where cmd like '%low on space%') > 0
begin
declare @sql varchar(200)
SELECT @sql ='select * from ##diskspace where  cmd like ''%low on space%'''
PRINT @SQL
exec master.dbo.xp_sendmail @recipients='Your ID', 
   @query = @sql,
   @subject = 'Disk Space Full'
end
drop table ##DiskSpace