Do you use Linux?

In all cases of Linux/Mac/Windows you can use a great app called HandBrake which will rip & encode a dvd (or video file) to several other different types. It also has presets for things like "ipod" which (I believe?) will also play in android phones and possibly the N900?

For Linux there is Hyper Video Converter and WinFF. I reviewed (older versions) of both here. I'm not sure WinFF and HyperVC will allow you to go directly from the DVD device.

So you can use things like dvdbackup and vobcopy to extract a DVD's movie title to a VOB file on the local drive.. and then run that through converters.

There is also K9Copy.

For windows .. there is DVDShrink. I don't link to it, because they won't let you download it from their website due to "legal" issues. You have to google it and find it.

That will only extract it to the HDD though, I don't think that will encode to a N900 compatible format.

Then of course, there is one of our own members Tablet Encode that will encode a video file to a tablet friendly format. It would work, in theory, on windows, mac or linux - since all of them, I believe, have mplayer/mencoder available.