Free is the tough part. But look at GEEXBOX on google.com
The problem is that there is no free one at large since a license fee must be paid to www.mpegla.com If you can solve the license issue, then you might see more free players. GEEXBOX is from a place that doesn't recognise mpegla's authority.
I have recently been given a laptop by my company however they decided to remove the software needed to watch DVDs. I have asked why but they will not give me a decent answer and will not put it on again! Does anyone know of a decent programme to download? Preferably free of course. Using Win XP.