Lord Evermore,
<< Most likely it's the mobile version, which I don't think you can get by itself, so no, you can't swap it out. You might be able to buy one from HP, but probably not. I'm not sure what interface the mobile P3's use now. >>
That is incorrect. You can buy mobile P3's individually however they are obviously somewhat hard to find. I know people that have done it before.
Whether or not you can replace it depends on what motherboard / processor package is used on your particular model. There are ones that use embedded P3's which can not be removed except perhaps by HP and there are also ones that are socket style where you can do a swap just like with a regular pc. Do some research on HP's site and try to find the technical papers on your system to find out which it uses if you can.