With great difficulty.
Premiere has neither a direct import/ripping tool for DVD, nor editing support for SD MPEG-2 - this is probably while most fan editors tend to use Womble or Vegas (though I personally favour Grass Valley's Edius program, which performs incredibly well with compressed sources like that, and it even has a direct import tool for non-encrypted discs).
At a push, you could rip the video streams first (with Decrypter or whatever) and then convert them into something friendlier like DV AVI - there are various video converter tools you can download, or if you're on the latest (CS4) Premiere, its standalone media converter should be able to achieve this.
Whatcha makin'?