Best budget 5.1 home theater system?
..For a rear-projection 51 inch television, also have a DVD player and satellite DVR hooked up
I would also like to know the name of the adapter that allows you to connect PC speakers to the television. I use to have my Klipsch 5.1’s hooked up to my TV but lost the adapter. 
The cable is a 3.5mm female to 2 rca male cable. Sometimes called a 3.5mm audio breakout cable. I've linked one below.
As for a HTIB, I don't think they're worth the money unless this is a bedroom system and it doesn't sound like one. Once one part of these systems breaks, you end up throwing the whole thing away and they seem to last about 5 years. DCM Cinema 2 system has gotten good reviews and is only around $400. That's just the speakers but if you add a decent Onkyo receiver for around $400-$500 you'll have the start of a system that will last and can be upgraded. If your budget is higher, check out the JBL ES20 speakers for around $1750 (5.1 channel speakers).
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The cable is a 3.5mm female to 2 rca male cable. Sometimes called a 3.5mm audio breakout cable. I've linked one below.
As for a HTIB, I don't think they're worth the money unless this is a bedroom system and it doesn't sound like one. Once one part of these systems breaks, you end up throwing the whole thing away and they seem to last about 5 years. DCM Cinema 2 system has gotten good reviews and is only around $400. That's just the speakers but if you add a decent Onkyo receiver for around $400-$500 you'll have the start of a system that will last and can be upgraded. If your budget is higher, check out the JBL ES20 speakers for around $1750 (5.1 channel speakers).
References :
http://www.thenerds.net/CABLES_TO_GO.Cables_To_Go_Value_Series_Audio_Y_Cable_1_x_Mini_phone_Stereo_2_x_RCA_Stereo_Molde.40424.html?affid=1&srccode=cii_9324560&cpncode=17-16221405-2&affid=3
http://www.hometheatermag.com/compactspeakers/1107dcm/