With the default report,you can get Count or list of PC’s from domain Eg: Computers in a specific workgroup or domain.
If you want to know the count of PC’s with specific role like standalone workstation a.k.a Workgroup computers,member workstation,member server,standalone server etc,use the below report .
I use property called DomainRole0 from V_GS_Computer_system view with case statement.
when 0 then 'Standalone Workstation'
when 1 then 'Member Workstation'
when 2 then 'Standalone Server'
when 3 then 'Member Server'
when 4 then 'Backup Domain Controller'
when 5 then 'Primary Domain Controller'
Count(*) [Total] from v_GS_COMPUTER_SYSTEM
group by DomainRole0
Here is the referral link which you can get information about domainrole and its values. http://msdn.microsoft.com/en-us/library/aa394102(v=vs.85).aspx