You can get Photoshop CS2 for PC/Mac for free if you have or register for an Adobe account from
here. The version is out of date, but the tools for restoration have not really changed much in the newer versions, so this one would work great. You can also get GIMP (GNU Image Manipulation Program)
here for free. It has the same type of tools as Photoshop, but is an open source program.
Of course there is the issue of learning a new tool. A good book to learn restoration in Photoshop is "Restoring and Tinting vintage Images" which can be found
here. I know the author, great guy,

lots of great examples. Use the code "JQZRUQ35" and get 25% off on the book, but don't tell him I told you that....