I presently am running WinXP from my primary internal SATA drive, and Ubuntu 14.04 from an external USB drive. I have installed a new internal SATA secondary hard drive. Is it possible to MOVE or COPY my USB drive's contents to the secondary internal drive, OR should I simply reinstall Linux from scratch onto the internal drive, run updates, and then copy my home directory from USB to the internal drive ? [I am planning to dual boot on the two internal drives by having Linux replace the primary drive's MBR with GRUB.]
You should be able to move your file system off usb with rsync. Boot into Ubuntu as you normally would (off of USB) and then mount your new SATA drive that you intend to move Ubuntu to.
once the device is mounted you can then copy everything over
That will copy your file system off of USB and onto your new drive. As far as setting up grub and what not, unfortunately I cannot help you there.
Disclaimer: I have not done this before as you are asking, but I do use this method to move the file system off of the SD Card of my Raspberry Pi and onto USB.
It is totally possible. What will vary is what lengths you are willing to go to in order to protect your windows drive from possible erasure. My plain-english solution below may not look very geeky, and it may seem more difficult but it will protect your installations from harm.
The following instructions are IMO the best way to do what you say you want to do:
The following instructions explain how to do something still better and safer: In my opinion, dual boot installations are just plain unsafe. For this reason I would advise you to purchase a hard drive tray system, assuming of course that this is a desktop and not one of those laptops with two hard drive bays, and literally swap hard drives depending upon which operating system you wish to use.
hard drive tray systems come in all flavors, ide and sata, and can be purchased for under $20. I would be happy to make recommendations.