Do I need to buy an amplifier in addition, if I buy one of these home theater systems?

-There are three different URLs:

http://www.frys.com/product/6598593?site=sr:SEARCH:MAIN_RSLT_PG



http://www.bestbuy.com/site/Samsung+-+Factory-Refurbished+1000W+5.1-Ch.+DVD+Home+Theater+System/1328701.p?id=1218250639230&skuId=1328701



http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l=en&s=dhs&cs=19&sku=A4796090&~ck=baynoteSearch&baynote_bnrank=0&baynote_irrank=0



Also, which one would be the best?They are theaters in a box. U get it all. But lower grade of prod in some areas. I would recommend buying all seperate. May cost a few bucks more, buy way better quality. I take alot of pride in my home sound. If I were u just go 7.1 thats the future, be ready for it.