I believe you should be able to press F11 or CTL+F11 when the system is first turned on to boot into the recovery partition. This will allow you to factory install your OS back onto your boot drive.
However, I would download something like Knoppix or Ubuntu Linux, burn the iso to a disc, then boot it ... you can then use *nix to copy off any data to say a thumb drive or removable usb drive.
For the best value, if your say upgrading from vista, get the WIn 7 family pack with 3 licenses, its around $160 or so on Amazon vs like $110 for a single upgrade license.