Is it possible to safely contain a virus - not letting it spread?

Note that a problem (the main problem) with solutions like VirtualBox, Vmware, or Windows Virtual PC, is that some (many) viruses are designed to spread to network shares and attached drives.

A solution to this problem is to make sure that your virtual box/machine has no network connections and no attached drives.

Which does make it rather harder to use, and much less convenient. But not impossible. Copy any software you want to test to the virtual box/machine, stop it, disconnect it. Restart it and install/test/use the software you want to install/test/use, then stop and discard any changes that have been made to the virtual machine.

Use Sandboxie. You can get it at sandboxie.com

Using another account will only help if you set the account as limited and the program you're trying to run doesn't request privilege escalation. Running your program in a sandbox like Sandboxie is much safer and easier.

When running suspect programs, you have to be aware that the program will infect the operating system of the computer, not just the user account.

To do so semi-safely, it would be best to run some sort of virtualization program like parallels or vmware or others which creates a virtualized instance - another copy of the operating system running partitioned. You could then boot the virtual OS, run the program and then later exit and throw away the virtual copy.

That said, it is highly desirable to NOT do this since it could do things like try to change your router settings or get other info about your LAN devices, damage or transmit info from files it can see and do other things - only limited by how much you allow the virtualized OS to see other things on your LAN.