system tables and indexes problem

        Re ,

    I hope someone will help me ...
I've a big problem with a database .

When i try a vacuum :
NOTICE:  Vacuum: can not process index and certain system tables
and i have to kill the process because i take all the cpu ..

When i try to access system tables :
- the select take an eternity and i have to kill him
- or i lose the connection

Is there a solution ?

Postgresql 6.5.2 on Linux .

        Thanks