P.X.E. in a wan environment

We have one NW 6.5 server with ZDM 7 installed in the main office.
Later all remote offices will get this.

But until more servers out I have a question:

Wil a PC in a remote site automaticly find the PXE server in the main
office?
We want to use Zen policy to put a new image into a PC from a local DVD.

Magne