If you just want to see Windsor Castle you can easily do it by train. And I'm not sure if private guides are allowed there. And not sure what you mean by area (do you want to see Runneymeade? there's really nothing there).

It might help to tell us ow little time you have and what your must sees are. It may not be doable on foot.

We are going out to see Windsor and then have some small villages nearby where our ancestors came from. The train wont reach those spots and it would be much more time efficient to go by car to the places we would like to see. I do not want to rent a car and struggle with directions and getting lost. So for our need a driver or driver/guide would be the way to go.

Sorry I don't know any driver/guides in London. But, to answer your second question, London a big place with the sights spread around. You wouldn't see much on a single walking tour. However, the highly-recommended London Walks (www.walks.com) has a wide variety of walks dealing with specific themes and neighborhoods.

If you wanted to see Windsor Castle, just take the train and do it under your own steam, as it were.

For your personal interest in the town and surrounding places, it might be worth contacting the local tourist information office and the local family history society for advice (you do realise that parish records and the like will be at the County Record Office in Reading?):
http://www.windsor.gov.uk/visitor-info/visitor-information-centres
http://www.berksfhs.org.uk/genuki/BRK/