tumblr in a subdomain

hey i want to put a tumblr in a subdomain.. so my main website ddd.com would still exist, but tumblr.ddd.com would redirect to my tumblr page.

i added a subdomain and added a A record to the tumblr servers.. it works sometimes, but othertimes it comes up with a blank "index of /" folder.

I emailed tumblr support and they said:
Hi, Nate. There is something going on with your domain name configuration. Make sure you only have one A Record for the domain and make sure you don't have any forwarding or masking enabled.
I dont think i have masking or forwarding (i didnt set any up at least), but it seems like the nameservers are conflicting (there are dreamhost nameservers that show up... i just added the new A server)

how can i remove the dreamhost servers for the subdomain only. is it possible? thanks

I don't think adding a subdomain was the correct approach. If you already have the ddd.com domain, you should just be able to edit its DNS records and add that A record.

-Scott