using ordinary connectors you probably have right now.
For more details, how to obtain free mmc device drivers, and installing various open source Linux distros on WRT54G wireless routers (and other routers and devices), go here:
This is the finished "SD floppy" connector, which has been running flawlessly inside a friend's wireless router for 6 months now:
Step 1: 01_floppy_cable.jpg
Step 2: 02_5.25in_floppy_connector.jpg
Step 3: 03_good_pin_alignment.jpg
Also, you can see that the ridge on the edge of the SD card slides firmly into the groove in the connector plastic pin separator, which aids card alignment (when the card is inserted using the connector even pins).
It causes no harm to insert the SD card backward, because the odd pins are not used in this application.
Step 4: 04_fully_inserted.jpg
Step 5: 05_new_sd_cable.jpg
For more details on where to connect the wires inside your wireless router, detailed links are provided at the bottom of this page:
A closeup of the connector at this point can be seen in the next photo.