Can I put Ubuntu 14.04 LOS on this? Dell site says only Windows 2003 server? KVM board blocks any upgrades by blocking the USB and CDROM device from working?
Yes, you can install a modern OS on this server. It's just about the oldest system that would support a 64-bit OS. (Intel 7100-series CPUs, I presume?)
Now, is it worth using this system? Not from a heat, power, noise or space/footprint perspective. But if you have it and want to use it... sure, go nutty!!
Ubuntu should install without issue or the need for additional drivers. Granted, you may not be able to get the OMSA driver suite to work on Ubuntu for management/monitoring purposes.
As for your KVM board, reset the BIOS settings to default or use an external USB CD or network installer for Ubuntu... I don't see why that would be a problem for you. Can you elaborate?
The supported operating systems are:
Microsoft® Windows ServerTM 2003, Standard x64 Edition;
Microsoft Windows Server 2003, Enterprise x64 Edition;
Microsoft Windows Server 2003, Standard Edition;
Microsoft Windows Server 2003, Enterprise Edition;
Red Hat® Enterprise Linux® 3 and 4;
SUSE® Linux Enterprise Server 9 EM64T SP2
Everything on this list is end of life, or shortly to be end of life.
You're on your own for installing any other OS. (And if you want to ask a question about that, you need to specifically ask about it and provide a lot of detail.)
My recommendation would be to put this beast back in the dumpster that it came out of.