If you have successfully installed your certificate, however you wish to make a backup with the private key, if you do not have full admin rights, Windows will not allow it.
You must give your self access to the MachineKeys Folder:

Open Microsoft Windows Explorer.

Locate the '%SystemDrive%\\Documents and Settings\\All Users\\Application Data\\Microsoft\\Crypto\\RSA\\MachineKeys' (assuming you have a clean install) folder.

There are several files located in this folder. Each file in this folder corresponds to a key container. Try to open each with Notepad.

If you receive an Access Denied error message when you try to open a file, open the properties of the file, and then take ownership of it. Reassign the Administrator account Full access.
Repeat step four for each file in this folder. You should then be able to start the System Attendant service.

If you cannot find the above folder, insure you can view hidden files and folders.

Note: This will only work for SSL certificates on Windows XP and lower. This also does not apply to e-mail certificates.