XP Home will allocate a drive letter to the memory card as it is inserted. If a second card is inserted, another drive letter will be allocated. Just look in My Computer to see the contents of each card.
When you want to eject the card, look in the System Tray (bottom right, near the clock), and you will see an Eject Drive icon. It looks a little like a memory card with a large green arrow above it. Right click the icon, and choose to 'Safely Remove Hardware', select the card (if you have more than one insrted, then choose Stop. That will avoid any file corruption.