You don't have a PCI-Express slot. You DID, but HP removed it. If you look at your MoBo diagrams, you'll see all those silver 'pins' above your white PCI slots; that used to be a PCI-E slot.
To fit your case, the MoBo must be the following:
- Socket T (LGA 775)
- Support P4 Prescotts
The board you chose won't fit; it's not Micro-ATX.
Bear in mind that you are currently running on integrated video. If the new MoBo you buy doesn't have an integrated video card, then you'll have to wait to buy a PCI-Express graphics card before installing the MoBo. I ran a search through newegg, and this came up as the only compatible board (try running your own search though):