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If it really is a MacBook, your wife's MacBook Pro DVD is not likely to work.
Insert the disc and start the MacBook while holding the C key. If it does not start from the disc, and goes right to the login screen as you have been seeing, or gives you a message to the effect "this disc cannot be used on this Mac" then try the links Limnos provided.
An underlying concern is whether the MacBook was legitimately sold, and not stolen. Sellers should always include the system installation discs, and buyers should always insist upon having them. No exceptions! The ability to troubleshoot and correct potential problems will be hindered without a system installation DVD.
You could try contacting Apple to see if you can talk them into selling you a replacement system installation DVD. They will need the Mac's serial number and some cash.
MacBook: How to find the serial number