at a minimum you probably need to think about a 3.0 system. When the soundtrack is Dolby Digital 5.1 so much of the dialog is concentrated in the center speaker channel, that not having one - or trying to create a phantom center with a stereo system, just won't work for many listeners.
No need to spend huge bucks, a simple DD5.1 a/v receiver like an Onkyo SR307 or Pioneer 519 will work fine. Toslink optical cable from the DVD player to the receiver with front 3 speakers enabled in the setup menu. You can then control the level of the center channel separately to drive the dialog.
http://www.accessories4less.com/make-a-store/item/ONKTXSR307BLK/Onkyo/TX-SR307-5.1-Channel-Home-Theater-Receiver/1.html
http://www.newegg.com/Product/Product.aspx?Item=N82E16882290094
and
http://www.newegg.com/Product/Product.aspx?Item=N82E16882290022
good luck
I respectfully disagree. I think, for best dialogue intelligibility, a pair of speakers is actually better than three speakers if the center speaker is going to be a horiz mtm. OTOH, the center speaker will lock the dialogue, however unintelligible, to the display, give one the potential for a wider soundstage without imaging dropout, and greater dynamic range by avoiding compression.
But, IMO, a vertical speaker, with vertically arrayed drivers, free in space, not resonating on a shelf, or suffering other diffractions and/or reflections, without being considerably above or below the listener's ears but rather at ear level, would make for the best dialogue intelligibility. Just my subjective opinion based on limited experiences.
Also, I cannot recommend entry level Polk speakers either for dialogue intelligibility.
For $500, there are options. That's plenty of money for a basic 2.0 rig. Heck, you could possibly hook up active monitors, with money in the pocket. Or perhaps a stereo receiver, from $80-200, whether Sherwood, Pioneer, Onkyo, and add a pair of Ascend 170Se. Or PSB B15. Or a lot of other speakers besides the Polks. JMO.