Hi Eogon,
Not sure if you resolved your question or not, so I thought I would offer some input.
The easiest method of determining which motherboard you can use is as follows...
On the bottom of the computer or under the battery, you will find the product number. It should look very similar to "GJ156PA#ABA". Also take note of the serial number.
Take those numbers and go to the following web page... http://h20141.www2.hp.com/Hpparts/
Enter the product number into the corresponding field and press the enter key on your keyboard. If the system says that no match can be found, then try the serial number in the serial number field.
On the next page, you will have a couple drop downs. Look for the one(s) that say "PC Board" or "Main Board" and choose the appropriate one. The resulting page will give you the part number and if HP stocks it or if you'll need to contact a reseller.
Hope that helps