there are differnt kinds of memory card but they are not hard to find. Is there one in the camera just now? They are usually an SD or XD which come in different sizes 16mb, 32mb, 64mb, 128mb etc Just go to your nearest photo shop with the camera
A quick Google of Praktica cameras seems to indicate that they use SD (Secure Digital) memory cards. If this is correct for your camera you will also be able to use MMC (Multimedia Cards).