Long story short had a fast computer - hard drive crashed - HP sent me a new hard drive - installed new hard drive today - now I have a sloooooooow computer. Why?!?!
Did they send you the recovery DVD's with the drive? Failing that have you downloaded the drivers off of the HP Website?
probably your drive is running in a "pio" mode which was used for oooold dos-times drives. you can try to reset it with this script: http://winhlp.com/tools/resetdma.vbs (rightclick, save as) .. it is for win xp though, not sure if it still works on newer versions. if not - google for "pio mode" and you should find some instruction on how to re-enable ultra dma for your drive.