3GB is sufficient to install a Debian system with knoppix. You cannot really control what you install. Once installed you can remove and add programs.

Is your partition a FAT partition? If so using partionmagic create a logical ext2 partion of 3GB. Then resize this by reducing it by 250MB or so. When asked wheter to reduce it from the FAT partions ssay no. Then you will be left with a free partition. Right click this and select a linux swap. Then write the cahnges to disc.
Now you can install Knoppix.