My win XP does not recognize my 4gb SD card

Have you checked if the SD card is locked before plugging it in the card reader's slot of your laptop? Then again, see if the specs of your laptop's card reader can do read a 4 Gigabyte SD card, sometimes they could only read 2 Gigabytes down but considering that its an HP, I think it should be able to read even up to an 8 Gigabyte or higher. Though our laptop does have some card reader slots available, I'd still us the connection cables included with our digital camera and plug the camera with the card to our laptop. It works fine for me. Just have to set up the digicam on the USB connection tweaks. At any rate, you can always go to the shop were you got your laptop or the store where you got your SD card, inquire about the problem that you are having and let them handle it. Both the laptop and SD card can be brought to the shops I guess..