This is what your system looks like
, right? So I guess you do not have a floppy drive, if you want card reader in front, or you will remove the floppy drive, well anyway here you can see
internal card readers, and you need reader with 3.5 dimensions, for it to fit instead of floppy drive.
As I can see, the readers are connected via USB interface, so you need to make sure to know how will you connect it (last I owned a desktop system it was about 6 years ago, since then - only noteboks, so I do not know if in modern systems there are internal USB ports or something).
About RAM, you can check vendors here:
It's best to choose PC3200 memory. If you would like to add memory, that is to add another 512MB to your existing memory, you need to make sure that only 1 of your existing 2 memory slots is occupied (perhaps you have both slots occupied by two 256MB chips), and then you need to make sure that you buy type of memory that matches your existing one, that is PC2700 or PC3200 (I'm not sure about other RAM properties though). So its easier just to buy 1GB RAM chip or two new 512MB chips, and forget what you have in your PC now