In my experience, every table has a row in sys.sysindexes that can be used to tell the number of rows in the table.

SELECT i.rowcnt, o.name

FROM sys.sysobjects o JOIN sys.sysindexes i ON i.id = o.id

WHERE o.xtype = 'U' AND i.indid IN (0, 1)

ORDER BY o.name

Because these values are stored in the system tables, this is not an expensive query.