You can't just set up linux on the usb HDD and then set the mbr to load that partition. The master boot record would be on the c drive and it would tell the computer to divert to the partition on the usb hard drive. And you say "like SuSE" but what distros do you have and which would you prefer to use?

If you tell me what distro and version, and what bios and version you have I'll try to help you.