Pointing me at some good documentation for it would help; I find the postgres site really difficult to extract information from. I've looked on two occasions but got fed up with lack of info.
Interesting. I find the PostgreSQL manual elegant, simple and orthogonal and I find the MySQL one a total cross-version jumbled mess :)
This is the URL you want:
http://www.postgresql.org/docs/8.0/interactive/libpq-exec.html#LIBPQ-EXEC-MAIN
You can use the PQprepare/PQexecPrepared combo to have separated prepare and execute steps. Or, you can use PQexecParams to simple execute a statement with separate parameters.
If you can show me some C code that does it, I'll install postgres and hack up something to make it work.
Just look at php-src/ext/pgsql/pgsql.c. Find the pg_prepare, pg_execute and pg_query_params function implementations.
The basic thing in PostgreSQL is that it uses positional parameters: $1, $2, $3 instead of ?, ?, ? or :var1, :var2, :var3.
Chris