Junk queries with variables?

I really have to be missing something here and this probably a *really* noob
question. I don't have a problem running little junk queries in the pgAdmin
query window(SELECT blah FROM blah, INSERT INTO blah, etc...), but I can't
figure out how to run queries with variables outside of a function. I just
want to use variables without having to go about creating and dropping a
function for every stupid little query I need to write. Example:

amount int4 := 1000;
earliest_date timestamp := current_timestamp;

SELECT ...

I always get the error: "ERROR: syntax error at or near "amount" at
character 1". What have I done wrong, or am I missing?

Thanks,
Steve