timespan arithmetic

Hello.

I recently posted this question on pgsql-novice and received no
answer. Undaunted, I'm trying again on pgsql-sql. Perhaps someone
knows at least where to start looking for an answer to this problem.
It's not in the FAQ, and I couldn't find an answer in the mailing list
archives.

I have a table that includes a column of type timestamp. I'd like to
formulate a query that returns, say, all rows no more than 24 hours
old, based on the timestamp. Trial and error got me this far (and a
perusal of the mailing list archives confirmed it):

SELECT * FROM table
WHERE loaded_time >= 'now'::timestamp - '1 days'::timespan
ORDER BY loaded_time DESC;

This works fine in PostgreSQL 6.4.2. However, another user of my
software, who has PostgreSQL 6.3.2, reports that he gets the following
error message:

ERROR: There is no operator '-' for types 'timestamp' and 'timespan'
You will either have to retype this query using an explicit cast, or you
will have to define the operator using CREATE OPERATOR

So. Is there a correct solution to this problem that works for all
versions of PostgreSQL--or at least, PostgreSQL versions 6.3.2 and
higher? Barring that, is there at least a solution at all for 6.3.2,
which may or may not be different from the solution for 6.4.2 and
higher?

Many thanks.

David