The brand is important as some ram is utter crap.. You're laptop uses the following type of ram: DDR2 - 800MHZ, PC2-6400, SDRAM Small Outline Dual In-Line Memory Module (SODIMM)
So my recommendation would be to do a little research and see which brand you think sounds the best to you then go from there..
If you really want to use the same brand that is already installed then you could always remove the "RAM Cover" and take a look at what brand they have installed in you're laptop.. Instructions for how to do this are available on HP's website. Just keep in mind that you don't HAVE to use the same brand that they did.. Though I understand some people like to keep things consistent and there's nothing wrong with that..