A more accurate query is...

SELECT

SO.Name

, SI.RowCnt

FROM

SysObjects SO

INNER JOIN SysIndexes SI ON SO.ID = SI.ID

WHERE

SO.Type = 'u'

AND (SI.RowCnt IS NULL OR SI.RowCnt < 100) -- nto 100% sure but I think rowcnt will never be null

and SI.IndID IN (0, 1)

A table will only have one record in SYSINDEXES with a value of either 0 or 1. This simply depends on whether (or not) the table has a clustered index.