You could install windows, autocad, etc, and boot via the usb drive. As you said, you'd need to set the USB drive to bootable in the BIOS. I would expect a performance hit running the OS over USB. Keep in mind that while indeed the system would be portable, you'd have to set every machine you wanted it on to boot from USB, *IF* it supports it.
You might be better off trying to make some menu files, or profile files, or even install files that install your dvb and lsp files to the local drive from your USB drive.