Select First N Rows Of Table

Let us say that I have a table with two sets of values as such:

Item Extension
--- ----
100023 1
100025 1
100025 2
100028 1
100029 1
100029 2
100029 3
[...]

Note that a given item number can appear multiple times if it has more
than one extension number.

I want to be able to select the first N entries as grouped by item
number. So if N = 3, that would return 100023, 100025 and 10028 with
their associated extentions. I would also like to be able to select
say, the 2nd through 9th entries grouped by item number.

I've tried something like this to give me row counts:

select rank = count(1), t1.item, t1.extension
from ItemTable t1 inner join itemTable t2
on t1.item >= t2.item
group by t1.item, t1.extension
order by rank

But that gives me this sort of result:

Rank Item Extension
---- --- ----
1 100023 1
3 100025 1
3 100025 2
4 100028 1
7 100029 1
7 100029 2
7 100029 3
[...]


Any suggestions would be welcome.