FUNCTION taking a record; returning a record?

Dear list,
I wrote a function that takes one parameter of a certain 'table type':

CREATE FUNCTION deserialize(serTable table1) RETURNS record AS ...

I whish to use this function in a query such as:

SELECT deser.* FROM deserialize(table1) deser(col1 integer, col2 integer),
table1 WHERE table1.field > [some_value]

Thus: have the function perform its operation on a SUBSET of table1,
RETURNING multiple fields.

I can't quite figure out how to put this together (other than passing the
table name and where-clause as TEXT)...

Any ideas? They are very much appreciated.

Regards,

Rob