DVD video is in the VOB format which you can't import into windows movie maker as you've discovered, rather than messing around trying to convert the VOB files into an acceptable file type to introduce into WMM you are probably best to download a free time limited fully functioning trial of a video editing software which will accept VOB input, as you are going to at the least cut the VOB's and join what you want together etc.
Arc Soft Showbiz DVD is worth a try for a trial download and easy to use.
I have Nero cd/dvd burning software, I don't know what equivalent software you have and in Nero Vision Express part of the Nero Suite if I select the Make Movie option I can import VOB and do a slight degree of editing, cutting, joining etc, so for that I wouldn't even need a video editing suite like Arcsoft for example.
Assuming the DVD source material isn't copyright protected, I would normally put the DVD into the pc's drive holding the shift key down for a while to stop it playing, go into my computer, right click the icon for the dvd, then select open and view the files.
Have a look in the Video TS folder and click on the VOB files to play them to find which one or ones you want to extract clips from and then drag them particular VOB's to a folder on the desktop, then take the DVD out of the drawer.
Then if using a video editing prog, or something like Nero Vision Express, import the VOBs into the program and edit them. Many video editing programs will import the VOB's direct from the DVD disc, but it can be a bit crowded when you only need a small few cuts from one or two vob files.
Working with VOB's after editing I would usually save the edited work as an mpeg2 file 720X576 at about 1MB sec, or 8,000 kilo bits per sec, or 8 mega bits per sec, whichever one of these options is given in the program, then later burn the file as a video DVD, or you could burn direct to DVD if given that option using these kind of quality settings.