If you need more than 16 you need to recompile Postgres, as it supports more than 16 just not in the default (stupid) configuration.
Unfortunatly OpenACS was made compatible with the stock install/RPM's of PG and their developers can't get it through their heads that someone may need more than 16 params.
If you are going to release your modules to the community you need to limit your parmeters to 16 and use overloaded functions. If you are not releasing the code to the community, you can do whatever you feel like.
