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There is a solution with just PL/pgSQL. Simple and elegant, too. Pretty advanced stuff, though.
Requires Postgres 9.0 or later (workaround for older versions possible).

CREATE OR REPLACE FUNCTION gesio(_tbl_in anyelement, _tbl_out regclass)
  RETURNS void AS
$func$
BEGIN

FOR _tbl_in IN EXECUTE
   format('SELECT * FROM %s', pg_typeof(_tbl_in))
LOOP
   -- do something with record

   EXECUTE format('INSERT INTO %s VALUES $1', _tbl_out)
   USING _tbl_in;
END LOOP;

END
$func$  LANGUAGE plpgsql;

Call (important!):

SELECT gesio(NULL::t, 't1');

t and t1 being the tables with identical schema.

Major ingredients

• Implicit cursor of a FOR loop instead of explicit cursor. That's generally preferable.

• Polymorphic types

• Object identifier types

• Dynamic SQL in plpgsql

• VALUES can take a row type directly.

A major obstacle to overcome is that variables inside the function cannot be defined as polymorphic type anyelement (yet). This related answer on SO explains the solution. Provides a workaround for older versions, too.

Basically I am handing in a NULL value of type t, which serves three purposes:

• Provide table name.
• Provide table type.
• Serve as loop variable.

The value of the first parameter is simply discarded. Use NULL.

Consider this related answer on SO with more details. The most interesting part being the last chapter Various complete table types.

SQL Fiddle demo.

Aside:
If your computations are not too sophisticated, you may be able to replace the loop with a single dynamic SQL statement, which is typically faster.