Instructions for installing Ubuntu on ARM Server reference boards is available here:
/Mustang: Applied Micro's X-Gene-based Mustang board
/ArmadaXP: Marvell Armada XP (12.04 LTS only)
/Calxeda: Calxeda ECX-1000 and ECX-2000 (discontinued, 12.04 LTS only)
/OMAP4: TI OMAP4-based platforms