declare @t tinyint
set @t =3
select right(replicate('0', 2) + cast(@t as varchar),2)
Ditto: on the cripping effect for numbers > 99
If you want to cater for 1-255 then you could use
select right(replicate('0', 2) + cast(@t as varchar),3)
But this would give you 001, 010, 100 etc