How Can I Recover previous OS X

Oops...I made a mistake...I didn't think anything would happen and that's when my problem began when "I didn't think". I have a MacPro and an iMac intel. The laptop is newer. I purchased that in 2009 the desktop was purchased around 2005????maybe. And here is what I did. I recently wanted to upgrade my operating system on my iMac, thinking nothing of it I took my MAC OS X 10.6 Snow Leopard disc that is for my laptop and inserted it into my iMac to do an upgrade....Now how can or if I can recover to the original OS X or do I purchase OS X 10.6 for the iMac. I don't want to do any further harm than I have. What is the best approach to this.

Thank you.[

A MacPro is a desktop. A MacBook Pro (MBP) would be a notebook - we'll assume this is the '09 computer.

The first Intel iMac was in '06 - we'll assume this is what you have and apparently you never upgraded it from the original OS X that it shipped with.

Putting the 10.6 disc that shipped with the MBP into the iMac would not have installed on the iMac and would not have affected the iMac unless you went into Disk Utility and decided to partition/format the drive prior to installing it. The discs that ship with Macs are system specific - they only have drivers for the system they shipped with, so they won't install on other types of systems.

Yes, if you partitioned/formatted the drive and you don't want to install the original OS back onto the iMac with the discs it shipped with, then you will need to purchase the retail version of Snow Leopard. You can get it for $20 shipped online from the Apple store.

Also note: If your iMac is not really an Intel machine, but is a PPC machine, Snow Leopard will not install on it.

Thanks for the info. Yes, I do have MacBook Pro and my desktop is an
iMac7,1 Intel Core 2 duo. The iMac did accept the MacBook Pro OS X
10.6. I did not go into disk utility to partition/format (I have no
idea what that is). The only thing wrong that I have noticed with my
iMac, since upgrading it with the MacBook Pro OS X is I can not
install anything, which is horrible.
I have never upgraded the iMac from the original OS X . If I purchase
and install the OS X 10.6 for my iMac all should run well?

Thanks Mac-Forums.

You can't install "anything". What does that mean exactly?
What happens? What have you tried to install? 3rd party downloads, apps that have their own installer, apps that install merely by dragging into the Applications folder, or from the Mac App Store?

Did you make a backup before you did the upgrade?
Do you have a backup now?

Doing an in place upgrade with the retail version of the disk, "should" take care of any issue that is specifically due to the upgrade with the MBP disk. If it's due to some other reason, maybe not.
We did have some systems that did not care for the upgrade to 10.6 all that well and a clean install was the way to go.

I should of been more specific when I said " I can't install anything". What I meant to say is that I cannot install any updates or even 3rd party downloads with their own installer.
Yes, a back up was done before I did that upgrade.
I will purchase the OS X 10.6 Snow Leopard from Apple and I feel comfortable that all will go well.

Thank you for helping me out on this. I appreciate you taking the time to explain.

In the meantime, you could go ahead and restore to just before the upgrade - particularly easy if using CCC or SuperDuper!.