newbie question: 'multithreading' longrunning postgres-queries from plpgsql-function.

Hi Group,

If a function (plpgsql in Postgres7.3) takes a long while to complete,
and only performs updates on tables, will other connections to the same
database just continue to function normally?

I understand that normal longrunning queries will run simultaniously,
but does that apply to plpgsql-functions too?

I need to know a little bit more about 'multithreading' in Postgres
before coding my application that way.
(I am not sure 'multithreading' is the right choice of words for the
describted situation.)

Thanks.

Regards,
Erwin