Garth writes some very useful SMS web reports so I copy them here sometimes:
http://smsug.ca/blogs/garth_jones/archive/2007/08/01/528.aspx

Declare @MS as int
Declare @VM as int
Declare @Real as int
Declare @Total as int set @Total = (select count(*) from v_GS_COMPUTER_SYSTEM)
set @MS = (select count(*) from v_GS_COMPUTER_SYSTEM where Manufacturer0 = 'Microsoft Corporation' )
set @VM = (select count(*) from v_GS_COMPUTER_SYSTEM where Manufacturer0 = 'VMware, Inc.')
set @Real = (select @total - @MS - @VM)

Select
  @Real as 'Real PCs',
  @MS as 'MS Virtual PCs',
  @VM as 'VM Virtual PCs',
  @Total as 'Total'