If you have to compress a dvd-video that large, you should use a different program than DVDShrink. Assuming you have this dvd decrypted and on the hard drive already, you can reduce the size using a free program called DVDRebuilder.
You can find the free version here: http://dvd-rb.dvd2go.org/
It requires Net 2.0 and AviSynth to work, but AviSynth is included in the full package. DVDRebuilder will be much slower than Shrink, but produces better quality on large dvds.