MSFT does not supply all drivers.
Head to dell.com, put in your SERVICE TAG and look for Windows 7 motherboard and that memory card reader driver.
My hard drive in my inspiron 1525 had to be replaced recently, and then installed Windows 7 Ultimate onto it. Everything seems to be working great except the built in SD/MMC drive. It can't find it, won't recognize when a card is inserted or even know it's there. Any ideas or suggestions?? Thanks!!