There is not much I can add about this machine that has not been already stated in the specs. The computer was a great deal for the money which at the time cost less than $350.00. It is a little under-powered but that was fine in my case because I had planned, (and have since executed), to change out the CPU, GPU, and PSU when it got here.
I have now an HP p6637C refurb with a 2.6GHz Phenom II x 4 and a Gigabyte ATI HD Radeon 5570 1 GB GPU, and a 300watt PSU. In addition, the computer was not capable to connect to a wireless network because it was not equipped with that ability. It only could connect via direct Ethernet cable. I was kind of surprised by that because I thought all computers were wireless Network-ready these days.
This computer was for my wife, (I have a much more powerful/faster desktop for my uses), and its position was perfect for an Ethernet cable to the router. But I still wanted it to be a wireless connection incase I ever wanted to rearrange the in-home office. So I also bought and installed a wireless Network card while I was installing the other stuff.
In the end, we have a computer for my wife that is fast enough to handle her "speed-clicking" without freezing up.
Bottom Line: As the HP p6637c comes straight from the box, it is a great deal for the price I paid, (see above). Keep in mind that if you don't plane to change anything as I have, the GPU is an "onboard" type and quite slow. The Anthalon 2.0 GHz CPU is ok but most importantly is the fact that it is not wireless ready. It's very easy to change that as well as all the other things I have listed.
Of course, I had these extra processors from previous purchases and really only spent and additional $11.00 for the Network card. Even so, the cost of a HD 5570 is about $40. and the PSU is about the same. This means that is you did want to go wireless and have better graphics, it would cost you less than $100.00. Meaning that you would have paid less than $450.00 after the upgrades.
I think it's all good either way.