You've probably figured something out by now, but here's my suggestion:
There are two options for getting your domain name to point users to your wordpress blog. You can map your domain name, or you can forward it (with masking so that your domain name will stay in the url box).
I have my domain name with godaddy, and this is what I'm trying. Perhaps even if you're not using godaddy, this example might be useful. Admittedly, I haven't completed the process yet, but it seems very straight forward.
First I had to re-map my domain name to godaddy's servers. (To undo the fact that I had mapped to wordpress.) It was easy because once I selected in the domain servers area that I wanted to forward this domain, godaddy reset the nameservers automatically. I didn't need to know their nameservers.
Next, I'll follow their instructions to forward this domain with masking.
Here are godaddy's instructions. Even if you're not with godaddy, maybe the terminology or the concepts will help.
Forwarding or mapping your domain
Setting nameservers for your domain names