I just took a look at the T400. There's the express card slot up top, and then the multireader slot below. What kind of card are you trying to read?
The multireader slot supports (I think) MMC, SD, SDHC, Memory Stick, Memory Stick Pro, XD and XD Type H. If you're trying to read Compact Flash, you'd need to get an Express Card - CF adapter. Other formats, not sure what's available.