With OS X 10.4.4 server and later, Apple has made NetBoot architecture-aware. NetBoot images support either PowerPC or Intel. (I can hope that with 10.5, it will be possible to create Universal images as well.)
You can set a default image for each architecture type, so all your Macs can still boot from your desired image when holding down the N key.
Here’s how it looks in Server Admin:
You’ll need either Apple’s System Image Utility version 10.4.4 or later, or Mike Bombich’s NetRestore 3.1.1 to create your Intel NetInstall/NetRestore images. Then move them to the server and select them using Server Admin, and you should be good to go!
Managing OS X 