Something doesn't sound quite right. Where on dreamhost are you seeing the change not reflected, and how long has it been since you made the change?
Panel changes do take 10-15 minutes to actually occur. Also be aware that a DNS change will occur slowly. Once the change begins to occur it takes 12-24 hours (possibly longer) as the DNS change propagate accross nameservers around the world. This means 2 delays, one short, for the dreamhost panel to make the change, and one longer (and out of the hands of dreamhost) as the change propagate to other nameservers.