Two HDDs, two OS
So i just built my new PC, put in a 2TB HDD and installed Windows 7 on it. Now though, I want to take my old drive from my other computer, and put it in this one. Thing is, it already has Windows Vista on it, and I haven't heard of a way to just straight uninstall that without having to format the drive. Can I just add that drive to my new PC and choose to boot off the Windows 7 drive? And is there any way to transfer all my Windows Vista settings and users and such from that drive to this one?
When you add the old drive to your new machine, there is one simple step to take to ensure it works as you wish. You need to boot the machine and go immediately into BIOS Setup, and look for where you specify the Boot Priority Sequence. It should already be OK, but just check. Make sure the sequence does NOT contain any reference to that old drive you just added. If you change anything, don't forget to SAVE and EXIT.
Set this way, your BIOS will never even try to boot from the old HDD, and all will be well.
Now we get to your trickier query.You want to try to transfer a lot of settings from the old VISTA drive to be used in Win 7. I'm not sure if you can do this after having done the Win 7 Install already, but check the Microsoft website for tools to help in "updating " VISTA to Win 7. There may be ways.
However, not so easy for actual application software. You did not exactly ask this. But for application software (for example, Word or Excel or Photoshop or ....) you cannot just copy stuff from one drive to another, and you generally cannot use in Win7 software previously installed on the old HDD under Vista. You pretty much have to re-install that software under Win 7 so that its Registry can get the proper settings.
If I were to go back to the old drive and just do an upgrade to Windows 7 with that, then would everything work normally without having to re-install all my programs? The thing is, this drive is rather old and it's already starting to have problems as it is, so I'm afraid that if I just leave everything on there, something could go wrong and I'd lose all my data. If there's a way to upgrade from Vista to 7, keep all the settings and data, and then just do a complete transfer on to the new drive, that would just solve everything and I wouldn't even have to use the old one.
Yes, what you suggest would work in most cases. See these M$ web pages for info on upgrading, what it does, and what types of upgrades are possible.
Specifically for an upgrade from VISTA to win 7, this page:
tells you which VISTA versions can be upgraded to which Win 7 versions, plus other info.
I presume you will want to install to your new 2TB drive, and probably plan to remove the old drive entirely because you're worried about its reliability. That can be done. You will have to pay close attention to which HDD unit is being used for the installation. Also you should probably use an option in the Install procedures that wipes out any previous Partition on that 2TB unit so it is completely empty before starting the actual installation. But make SURE you wipe out ONLY the new 2TB unit, and not the old one!!
You MIGHT have a problem after it's all working. With most installations of Win 7 (I'm NOT sure whether this applies to an upgrade, but I assume it will), it does a process designed to help you out of trouble later. IF it finds a second HDD in your system (and in your case, it will), it places a special set of system backup files in a semi-hidden spot on the second HDD. From then on, every time the system boots, if it has a problem with a corrupted or missing system file, it automatically goes to the safe backups on the other drive and restores good copies from there, then completes the boot process. Very nice way to save you a lot of frustration if it ever happens. BUT this also means that, every time it boots, the system will verify that those backup files are still available, and it they are not (like, if you have removed the second drive) it refuses to boot!
Now, there is a way to fix this problem. Basically, after you have removed the second HDD and can't boot because of this error, you can use your original Win 7 Installation CD to fix the problem by placing a new set of backup files in a semi-hidden spot on the only remaining drive (the boot drive) in your system. (Having them there is not quite as safe as having them on a separate HDD, but it's still pretty good.) Check the M$ website for "Startup Repair" in Win 7 for details.