It's very easy to install the OS on a separate drive.
During installation, simply click the appropriate drive's icon and let it install. To "dual boot" you can either choose which drive from the "Startup Disk" panel in the System Preferences or you can hold the option key as you're rebooting.
If you have the extra drive sitting around idle, just give it a try. Using a faster drive does not make *everything* faster, but it does make disk-intensive processes like launching applications and opening and saving large files perform more quickly.