UbuntuLTSP (https://help.ubuntu.com/community/UbuntuLTSP) allows to boot thin clients via the network from a main Ubuntu LTSP server and run Ubuntu as if installed on the thin client. I tested this successfully using an HP Thin Client from a standard (as in not modified in any way after install) Ubuntu LTSP install (LTSP option available on the Ubuntu alternate install ISO). Pretty cool!
Took me a couple of internet searches to figure out but in order to boot a Thin Client from Ubuntu LTSP using PXE, here are the DNSMasq options required in DD WRT (ubuntu-ltsp and 192.168.1.78 are the name and IP address of the Ubuntu LTPS install). dhcp-no-override dhcp-boot=/ltsp/i386/pxelinux.0,ubuntu-ltsp,192.168.1.78