indices

Hi,
   I had learned in theory that Hash indices are used for "=" and
B-tree for "<" ,">".

    explain command doesn't tell us which index it is using. Hash or
Btree?
Also,
    should a following query
     "id < 1243" invoke a index ? (assuming there is an index on id).

    I have seen Postgres using Seq scan. Is sequential scan done afer
getting the first
page for "1243"?

Sandeep