I'm not sure what OS you're using.
For myself, I'm on Linux, and I have a large array of tools that I use for this.
On Windows, I think the common approach is to use something like
DVD Shrink to rip the DVD to your harddrive, convert it to an AVI, then perform screen captures on it (in Windows, Alt+PrtScn works wonders).
Doom9.org has some good resources for ripping DVDs and converting them to AVIs. One that it mentions is
CloneAD, which looks like what you want.
As for resizing pictures, a good general purpose image editor is IrfanView. However, if you're going to make a screen capture comic, you'll need to learn a more powerful editor, like Photoshop or The GIMP.
Let me know if you need any more details.
