Thanks guys, I narrowed it down to the NIC on the server, some wierd conflict with the onboard SCSI controller, I changed the card and moved the card to another PCI slot, all is fine. The machines boot up in under 10 seconds, I'm quite impressed.
I am however having issues with the graphics on the older machines. I think I need to write out a full modeline for them instead of just passing a res to them. No matter what supported res I use, the image appears only on the middle third of the monitor, just squashed down. no problem on the other cards. I have tried switching the monitors round to ones that didn't have the problem, so I'm guessing its a Graphics card issue. Shame I'm a total linux noob and dont know what I need to enter in a modeline to solve this, but I guess I'll figure it out from a tutorial somewhere.
Thanks a lot