If you want Q6600, You will need to upgrade Mobo and RAM minimum. (assuming you re-use HP case + PSU)
Your Mobo from old machine not supporting Q6600.
intel Q6600
http://www.newegg.com/Product/Produc...82E16819115017
Cheap Mobo: Foxconn M7PMX-S
http://www.newegg.com/Product/Produc...82E16813186140
RAM: OCZ Platinum Revision 2 2GB
http://www.newegg.com/Product/Produc...82E16820227139
And you may need IDE to SATA card if you re-use your old Optical drive and HDD