Datatypes in PL/PSQL functions with multiple arguments

Hello-

This is my first foray into pl/psql so forgive me if I sound totally
incompetent.

I've been writing a few functions, and have come across some screwing data
typing issues.

When creating a function which accepts a single argument, things work just
fine, variable can be used throughout the function as expected with no
modification.
When creating functions containing two or more arguments, I have to
explicity cast the arguments whenever I use them (loading/casting into
another variable is an option, haven't tried though) to prevent runtime
errors. The functions get called just fine, but then run into problems using
any of the given arguments.

Has anyone had any experience with this? Please advise!

Thanks!
Benjamin

select version();
version
--------------------------------------------------------------------------------------------------------
PostgreSQL 7.4.7 on i686-pc-linux-gnu, compiled by GCC gcc (GCC)
3.4.1(Mandrakelinux
10.1 3.4.1-4mdk)