If I install a second hard drive with its own operating system will I have in effect two separate computers in one PC? I am trying to save the space of buying a second computer for my daughter to use without worrying about her accidentally corrupting my files. I also don't want to spend the money on a separate laptop.

Rather than going to all this expense, have you considered simply setting her up her own limited account.
At least this way she is unlikely to do any damage at all, and it will save you a headache.

To answer your question, YES, what you describe is possible.

You need not keep two desktop at your home because instead of buying two computers you can create two account in your PC and make your daughter's account limited so she cann't delete releated to windows files and you can login as a administrator, I think this the best way to deal with your problem.

Though to bring up a negative point to the accounts... Even as a non admin she can still get a virus that affects the whole PC.

An option that may work for you is that walmart(last I saw) had a 200$ beginners laptop, or you can check your local papers for lower end PCs and probably get a whole PC that is older for under 100$ and then you don't have to worry about her messing up anything in any way on yours.

Though in all ways giving her own limited account is the easiest and cheapest solution.

No need to buy two computers because you can create two accounts in your computer. You can create a limited account for your daughter and your account will work as a administrator.It'sa good option to save the money.

How to create a account:
Go to control panel>user account>click create a new account>Type the name that you want to use for the account and then click on next>select the desired account type and then click create account.

Two separate hard drives with separate OS will require you to install and configure a boot manager or else you'll never see the second OS unless you change the boot order in the BIOS.

Your best bet in every bit of honesty if you're that worried about your daughter doing something that might cause your computer to get a virus is to create a Virtual Machine for her. Set it up like you would set anything else up and then snapshot it. That way if she does do something to the VM, there's not real loss, just restore the VM back to the snapshot you made of it prior to it crashing and she's easily up and running again. It's the same concept used with thin clients or kiosk style machines.

Can I ask what makes you think your daughter will "corrupt" your files. Maybe an alternative is to teach your daughter safe browesing and teaching her the concepts of viruses and what they can do and how to prevent them. I would simply create another local user account and se permissions on the folders you don't want her to touch.It' rather very simple and as long as you have Anti-Virus, Anti-Spywre etc... then you should have no worries. What is she doing online anywasy, playng games, myspace, Facebook etcc...

Rick

And as NeedKarma said if you install the second HDD hen you'll most likely need to install a boot manager to choose between the OS'. I said most likely because some OS' (Linux distro) install boot managers with their OS' ie: Ubuntu. Or every time you want her to use the computer just use a liveCD LOL :)