Core 2 Duo is not actually 2 physical cores but they are amazing chips. There is basically 2 chips inside the 1. The clock speed (2.4ghz) has dropped but it's not about clock speed anymore, it's about how much gets done in cycle. I went from a newer Pentium4 4ghz (overclocked) to this 2.4ghz and its shitting on it.
As for price you can see on the links to get an idea but here's what I paid:
E6600 - 309.99
Asus P5W motherboard - 166.99 (open box but everything was sealed so it may have been new)
XFX 7600 GS - 96.37 ( - $40 mail in rebate = $56.37)
2GB ram (bought in Feb) - $255.95
had the lian-li case, 74gb Raptor, lightscribe burner, antec power supply and Scythe heatsink already. I spent $616 on the new stuff (including other case & ram) so I could sell it to my friend for $500. So thats $116 to upgrade then there's $80 in rebates so I end up spending ~$36 to upgrade
