Ok, so in between admiring my daughter's artwork an eating my lunch, I tried to sort out the PXE boot of the Sony Vaio. I'm suspecting the NIC... hardware is a Atheros AR8131 chipset which I'm lead to believe requires the atl1e kernel module similar to what's descirbed on the Unrecognized NIC wiki page
I followed the basic download and install instructions from http://joefleming.net/2010/05/26/atheros-ar8131-and-linux/
which is a great resource containing a new link to the driver source (wiki page link appears outdated so I guess I should update it).
But.... still no dice on the boot (even after modifying the modules file and recreating the initramfs). Of course I still don't know if it is certainly the NIC causing problems but it seems likely considering others have had this problem. I'll see if there are any tftboot logs or similar that can give more info. Maybe I should try windows standard maintenance procedure (reboot) on the router...