Assuming you have a "vanilla" NSLU2 (ie straight out of the box) the process to replace Linkys firmware with the Unlsung firmware is straight forward.
- REMOVE HARDDRIVES !!! This is important
- Access the NSLU2 web interface administation page (default is 192.168.1.77, but the IP will be dependant on your network)
- Enter the Administration menu link -> Advanced -> Upgrade
- ENSURE HARDDRIVES ARE REMOVED!!!!!
- use the web-interface to browse to where the firmware is found
- click upgrade and wait [approx. 5 minutes]
Once the firmware has been updated and the NSLU2 has rebooted you should now see the web-interface page has changed slightly
- the Linksys logo is now the Unslung logo
- firmware version top-right is that of what has been uploaded
- centre-bottom there is a label stating that the NSLU2 is running from internal FLASH (need to unsling next)
Now if you already have a version of Unslung in the NSLU2-FLASH then the update procedure is a little more involved