Photo by Indi Samarajiva.
Why wouldn't you want to use the restore disc? Your computer doesn't just have Windows: it also has free trials of several programs, various toolbars, and other bloatware that slows down your system. You need an install disc for Windows so that if it becomes necessary to reinstall you won't have to spend an hour removing unwanted software.
Luckly, you can download full ISOs (disc images) of the various types of Windows 7 from Microsoft and Amazon.com. These ISOs were put there to be freely available for customers who purchase copies of Windows 7 online, but if you have a legit product key there is no reason you can't use the ISOs to make your own Windows install disc. Tech blog My Digital Life has collected several download links for all versions of Windows 7. See the link below to download.
Windows 7 ISO x86 and x64 Official Direct Download Links [My Digital Life]