Having similar issues since I upgraded to Lion on my Mac Pro 3.1. Tried several workarounds after geting the "No Boot device available":
Used Boot Camp Assistant first/ download drivers- no luck
In my later searches I find out Apple only supports up to BCA 4 on the 2008 Mac Pro
-Created a USB windows installer with the Windows utility from a Microsoft download site and ISO- not recognized- I enabled USB boot option by adding the BootRom version to Boot Camp Assistant with XCode- No Luck
-Installed 10.6 w/ combo update on a separate drive and gave BCA3 a whack, only to realize the Win Drivers are only to be found off a 10.6.8 disc- since 10.6.3 was the last retail version, I had to use System Image Utility to rebuild a 10.6.8 installer disc via NetInstall.
SO I ran BootCamp on Snow Leopard and when it goes to reboot- same thing. this happens with eitherthe Win 7 Pro or Home Premium, which I put in both the Superdrive, and the secondary optical (Blue Ray burner) drive. IN the SD it spits out the installer and gives me the black screen of death.
Zapped the PRAM for giggles- no luck.
Out of ideas. Anyone?