the psu's mentioned throughout this thread is based on an ATX form factor, so they should fit inside your case - you will need to do some cablemanagament once you have things inside the rig.
if you've owned a GT220, previously, then the new GPU will drop in nice and cozy in your case.
hyperthreading - google it.
took the picture from a site but it's the same pc .
are you defi sure? many times out of none, the OP slapped him/her-self for "thinking" they looked the same and bought parts off the shelf only to find out that HP have proprietary parts inside there silly lil cases.
take a pic of YOUR case and keep us posted.