There are other, more specific ways. They depend on what you need: integer or numeric? What is the range of values?
You can read some solutions here: https://groups.google.com/group/microsoft.public.sqlserver.programming/browse_thread/thread/8d02d3cf475a7dd3/b93786735e1f0ad3
The solution for checking an integer is this:
CREATEFUNCTION dbo.IsSomethingInteger(@num VARCHAR(64)) RETURNSBITBEGINRETURNCASEWHEN (LEFT(@num,1) LIKE'[0-9]'ORLEFT(@num,1)='-'ANDLEN(@num)>1) ANDPATINDEX('%[^0-9]%', SUBSTRING(@num, 2, 64)) = 0 THEN 1 ELSE 0 ENDEND
Gert-Jan