DVD Shrink makes it pretty easy. http://www.mrbass.org/dvdshrink
There's a lot of instruction on that page also, but basically what you want is the Re-author button, then drag the title over to the left, select the chapter you want or you can also go by frames to adjust it if you want. Then click ok. You need to drag the same title over each time and do it again in the order you want them, if you want more than one from the same DVD.
Now, for doing a compilation from more than one DVD, you need to do this for each one until you have all the tracks you want saved on your hard drive. Then open DVD Shrink again and select re-author and this time, browse for and add each of the separate titles it made before into the left side. When you have them all there, it will make a new DVD with your tracks in the order you want.. however, they won't be presented as one whole title.. they will stay separate, however nearly all players will play the titles in order one after the other and many will let you skip ahead and even select a specific title.. no menus though of course :)
Hope that helps. I suck at explaining stuff so feel free to ask anything if I've confused you :)