Try this:
http://www.technical-assistance.co.uk/kb/usbmsd98.php
Or this:
http://www.msfn.org/board/topic/43605-maximus-decim-native-usb-drivers/
Or this:
http://www.wintricks.it/faq/usbpen98.html
http://www.wintricks.it/download/wtgenusb.zip
Or this:
http://www.ehow.com/how_6691060_install-storage-device-windows-98.html
The 15-in-1 card readers might also use the same USB mass-storage-device
class of drivers that USB memory sticks do.
Post back here if none of those work.