Quering by Regular Expressions stored in table

[Allen Fair <dba@xxxxxxxxxxx>]

Hi! I have a table with a character column (called match_regex) 
containing a POSIX regular expression, hoping to have Postgres use it 
while evaluating the "where" predicate. The following error occurs:

SELECT *
from patterns
where 'blah blah blah' ~ match_regex;

ERROR:  invalid regular expression: quantifier operand invalid

We are using Postgres 7.4.8. I just tried the above on Postgres 8.0.4 
and it seems to work! Is there a way to do this on my older version? If 
not, maybe I can leverage this to get Postgres upgraded ;-)

Is seems that I need a regular expression type on the right of the 
operator. Perhaps I can cast this 'character varying(100) column' to a 
regular expression type if there is such a thing... though I have not 
found one in the docs?
  where 'blah blah blah' ~ match_regex::regularexpression;

Thanks,
Allen