I'm guessing an Acer Aspire laptop? If so Pyroflea is correct BUT You might find you need to install a dedicated driver for your hard disc controller. Now hopefully this is included in Windows 7 but it might be worth checking the Acer site for drivers.
The other one to watch for is that OEM CD's seem to expect a blank disc, if the disc is formatted then it can complain. This is easy enough to get round by using something like GParted liveCD, you need to remove all existing partitions on the disc. I'd not worry about this though unless you have an issue when trying to install.