I'm working on that right now for a 50 node HPC using CentOs (looking at switching to Ubuntu) but I'm having real problems with getting a boot image -- well, booting.

Does anyone have some experience on a diskless/stateless boot solution with Ubuntu?

My objective is to install an image to a RAMdrive and run it from there. Since no data needd to be stored or kept, rebooting the system would be the same as a brand new system. Most of the literature I've been working with require an NFS or HTTP server to serve up a root FS. I'm looking to avoid that if possible - I was hoping to serve up the image as one big initramfs.img stuffed into RAM.

Here's my current detail:
Main system installed and working well: CentOS (2.6.32-279.19.1.el6.x86_64) but I'd use Ubu 12.10 or 12.04 if there's a recommendation either way)
PXEboot working well with tftp-server (0.49-7.el6)
DHCP is serving the PXE boot server information and the client is getting the menus and downloading the vmlinuz and whatever image file named.
dracut-kernel and -network installed (004-284.el6_3.1)

Here's my PXE detail:
kernel Node/vmlinuz
append initrd=Node/initramfs.img root=/dev/ram0 ramdisk_size=524288 rw ip=dhcp

The problem I'm hitting is that the root filesystem isn't mounting properly. I get following errors:
dracut warning: No root device "block:/dev/ram0" found.
or (depending on PXE variables)
RAMDISK: Couldn't find valid RAM disk image starting at 0
No filesystem could mount root

This has been driving me nuts! Does anyone have any advice? Is PXE/RAMdisk a pretty straight-forward thing with Ubuntu?