how to do plpgsql?

When trying to do some of the examples on
http://www.postgresql.org/docs/postgres/c40914344.htm

I keep getting:

ERROR:  Unrecognized language specified in a CREATE FUNCTION:
'plpgsql'.  Recognized languages are sql, C, internal and the created
procedural languages.

version is:PostgreSQL 7.0.3 on i686-pc-linux-gnu, compiled by gcc egcs-2.91.66


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Joseph Shraibman
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