Originally Posted by j0rpi
Ah, the old P4 which had HT. I used to love these. I have been offered a 2.8GHz for ~$9. It's supported by this PC. But i don't know if this motherboard accepts the HT version of it. (FYI - It's a Compaq Evo D510 SFF) The 2.8GHz P4 is supported since some versions of this PC shipped with it. So the best choice would be to install the non-HT one.
Oh, ok, I guess that is the safest choice then. I just searched on ebay (UK) for the 3.06 socket 478 P4 and found quite a few. They are selling for good prices, cheapest being Â£8.99 (only UK though) and from Hong Kong with free shipping starting at $15.99 USD.
Just found this on the HP/Compaq page for your model
NOTE: * Hyperthreading Support - Systems shipped after February 1st, 2003 will include support for Hyperthreading. To take advantage of Hyperthreading, the system must be configured with a minimum processor speed of 3.06GHz. HP has performed qualification testing under both Windows XP Home and Windows XP Professional. HP strongly recommends that customers upgrade to the latest version of the Microsoft Service Pack for these operating systems. This will ensure the best possible user experience.
You can check to see if your system qualifies. There should be date somewhere on the computer case.