Was able to partition and install Linux Mint 8 and now Isadora 9 from the Live DVD to the Seagate FreeAgent USB drive out of the box. I used entire 230 Gig drive. The dual-boot HP laptop system boots and performs fine with boot-loader on the sda1 or main laptop "c" drive.
**Special note: It is important to remember that installing your system on a USB drive will usually require a longer boot sequence/time but after boot the system performance impact should not even be noticed if you have a reasonably fast USB drive and the 2.0 USB spec.
Boot time with pre Grub 2 was faster and if you do some tweaking can slightly improve boot time but it is NOT worth (IMHO) the chance of introducing instability and/or a system upgrade issue which I had encountered on a previous installation. If it's not really broken don't fix it.