check (constraint) on point data type?

["Jill" <jill289(at)hotmail(dot)com>]

Hi,
I'd like to limit the values that can be added to a field.
The field is of type 'point', and I'd like it to reject any values less than 0 or bigger than 1 (i.e., accept only points with values like (0.4, 0.26)).
Let's say I try to define the upper boundary by doing:
ALTER TABLE "public"."locations"  ADD CONSTRAINT "up_boundary_chk" CHECK (location < (1,1));

but it fails.
What am I doing wrong?
I'm using Postgres 8.2.4.1
Thanks!
Jill