Changing collation for tempdb and model

Hi,
I've got a production server with the default collation
and User DBs with the different collation.
Now when I create temporary tables and compare with the permanent ones
we have collation problems. Is it possible to change tempdb ( and
model) collations ?
Would I need to change master and msdb collations as well?
Can I change the master collation? What about all the tables that
already exist in these system databases?
Is it fairly straight forward to change collation for tempdb and model
or it might cause problems in the future - I obvioulsy don't want to
mess up with the production server

Thanks a lot