I believe you will need to edit the report. I use Report Builder 3.0, so this is how I would edit a report to add Count... Using the default report "Computers with specific software registered in Add Remove Programs"...
-open Report Builder 3.0, Open the report.
-Save As the report to a new name (in case I mess up)
-Click on a field in the table, like [netbios_name0], so that the table active.
-rightclick on the row indicator (the grey thing on the left). Select "Insert Row, Outside Group - Below"
-right-click on the empty field under [Netbios_name0], and type in the word "Count:"
-right-click on the empty field under [SiteCode] and "Expression..."
-in the Set Expression for value, leave the = sign, and add Count( at the bottom, in Category click Fields, and select a value to count... like Netbios_name0. At the top, close it with the )
so you'll end up with =Count(Fields!Netbios_Name0.Value)
Hit OK. and "run" the report, see if it works.