Now you can turn your NSLU2 into the full-fledged USB Server. Just install the special build USB Server for NSLU2.

You need to install OpenWrt Kamikaze Linux into your NSLU before installing USB server

You can download OpenWrt Kamikaze from here:
Download OpenWrt Kamikaze

You can download USB Server for NSLU2 here:
Download USB Server for NSLU2

Follow these steps to install USB Server on NSLU2:

for OpenWrt Kamikaze 7.09:
ipkg install kmod-usb-server_2.6.21.6-1.90-ixp4xx_armeb.ipk
ipkg install usb-server_1.90_armeb.ipk

for OpenWrt Kamikaze 8.09
opkg install kmod-usb-server_2.6.26.5-1.90-ixp4xx_armeb.ipk
opkg install usb-server_1.90_armeb.ipk

More detailed information how to use above products you can find here:
How to use USB Server for Linux v1.9