Try this and compare it to the task pad view in Enterprise Manager.

 SELECT AA.name, AA.filename, -- AA.dbSize,

  BB.name, BB.filename, --BB.dbSize,

  (AA.dbSize) * CC.low / 1048576 AS DBSize, -- This is the total database size.

  (AA.dbSize) * CC.low / 1048576 - AA.AvailableSpaceInMB AS DBUsedSpace,

  AA.AvailableSpaceInMB as DBAvailableSpaceInMB,

  (BB.dbSize) * CC.low / 1048576 AS LogSize,

  (BB.dbSize) * CC.low / 1048576 - BB.AvailableSpaceInMB AS LogUsedSpace,

  BB.AvailableSpaceInMB as LogAvailableSpaceInMB,

  (AA.dbSize + BB.dbSize) * CC.low / 1048576 AS TotalSize,

  AA.AvailableSpaceInMB + BB.AvailableSpaceInMB as TotalAvailableSpaceInMB

 FROM

 (select name, filename, convert(dec(15),size) as dbSize,

  size/128.0 -CAST(FILEPROPERTY(name, 'SpaceUsed' )AS int)/128.0 AS AvailableSpaceInMB

  from dbo.sysfiles

  where (status & 64 = 0)) AA CROSS JOIN

 (select name, filename, convert(dec(15),size) as dbSize,

  size/128.0 -CAST(FILEPROPERTY(name, 'SpaceUsed' )AS int)/128.0 AS AvailableSpaceInMB

  from dbo.sysfiles

  where (status & 64 <> 0)) BB CROSS JOIN

 (select low

  from master.dbo.spt_values

  where number = 1

   and type = 'E') CC