Trouble playing DVD movies

I just inherited an HP notebook, Pavilion ZE5375us, from my mom (who had to upgrade, even though this notebook is just a few years old) as I needed one for school. She mentioned that she never could get it to play DVDs, but the CD-Rom part worked fine.
It does have a DVD reader (QSI SBW-241) in it. I spent a better part of today downloading a file for it. I was able to get a DVD to play,but it was a data DVD, not a movie. I have InterVideo WinDVD 4 installed. The microsoft website is telling me that the WinDVD 4 decoder is not longer valid. So, I downloaded the free trial of WinDVD 7 (to make sure that is what is going on) and downloaded Media Player 10 to go with it. So far, I have not received an authorization code from InterVideo… I just want to play a movie on my computer. I don’t even know if my DVD drive is capable of DVD-R… is there any free decoders out there for Windows XP that I could download to just play a DVD movie? Any help would be greatly appreciated.
Thanks,
Terri

Update Frimware.
http://h10025.www1.hp.com/ewfrf/wc/genericSoftwareDownloadIndex?cc=us&lc=en&softwareitem=ob-24494-1&jumpid=reg_R1002_USEN
If that doesn’t work. Try VLC Media Player to read the dvd.

Media Player Classic with ac3filter and ffdshow should do it. Google for those three.