All Dell PC's come with a reinstallation CD, but then it was purchased from Costco, so I have no idea. It might be worth contacting them for it.

The more software you install, especially software which starts with Windows, the slower your PC will become. Even when software is removed, it often leaves some mess behind. There are tools, as suggested in the Performance guide that really does help, but a reinstall gives you a fresh installation, with nothing installed. So, it is important before you do that to make sure you have a copy of all your important files and software.

EDIT: Marked as Answered.