First you need to download MakeMKV from here http://makemkv.com/ or use a PC in school that has the program pre-installed.
This is a very easy program to use and if you read the short instructions, you will know everything you need to http://www.makemkv.com/onlinehelp/
Basically, you are going to copy the DVD (or parts of it) onto the hard drive of a PC, so that you can then edit sequences from the film in an editing program such as Moviemaker or Premiere Pro.
Rather than copy all the DVD (which takes up a lot of space on the hard drive) you can just copy the "titles" (sections of the DVD) that you need - these contain the "chapters" (or scenes) that you will use in your presentation.
Make sure you choose the destination folder for the video so that you can find it once the "conversion" (save) has taken place.
After you have saved the DVD titles to your hard drive, go the destination folder. You will see that the video is saved as a .mkv file. You need to right click this file and rename it by changing the .mkv part to .mpg.
Now you should be able to import your .mpg file into an editing program and trim the sequences that you want for your presentation. Bear in mind that if you try to import a complete film into your editing program in one go, it will probably crash it! Whenever you are editing, remember to save regularly - editing uses a lot of RAM and programs frequently freeze.
Once you have finished editing, you can export ("Save to my computer" - Moviemaker) your clips into a format that will allow you to insert them into Powerpoint or Open Office Impress. For example, if you edit in Moviemaker you can export your sequence as a DVI-AVI (PAL) file which will open in Powerpoint. In Premiere Pro you could export as H.264, MPEG or WMV (Windows Media Video), all of which should open in Impress. WMV should open in Powerpoint as it is a Microsoft file.
A good explanation of supported file formats in Impress can be found here http://www.tcaps.net/Portals/0/technology/training_docs/OpenOffice/ImpressVideo.pdf
To add video to Impress you need to "Insert" - "Movie and Sound". Make sure that you save the video on to your memory stick and insert it from the memory stick, otherwise when you come to do your presentation the video will be missing. When you save the presentation, save it as ODF Presentation (.odp).
To add video to Powerpoint, you need to "Insert" - "Movie". With Powerpoint you can embed your videos in the presentation so that you don't have to carry separate video files with you - everything will be combined. To do this, you first have to click on the 'Office button' in the top left of the screen. Then hover your cursor over 'Publish' and choose 'Package for CD'. A box appears; click on 'options'. Check (tick) the 'linked files' option. Click 'ok'. Then click 'copy to folder'. Choose your title and destination and click 'ok'. Click 'yes' when you are questioned about linked files. Click 'close' once the files have been combined into one and you are done! You now have a single folder with your presentation and video. When you open the folder and click on the Powerpoint file, it will have your video embedded in the presentation.
Good luck! It may require a little trial and error, but you will get there if you persevere.
