When my linksys arrived it was already running a non stock firmware Tomato Version 1.27vpn3.6.4b664ba6 now as a previous user of dd-wrt I decided I would go back to that. First off it's a bad idea to go from one non stock f/w to another, stock to non stock gives you the best chance of an upgrade without bricking. 

So I followed this procedure

Hard Reset (aka 30/30/30 reset):

The following procedure will clear out the NVRAM and set dd-wrt back to default values:

• With the unit powered on, press and hold the reset button on back of unit for 30 seconds
• Without releasing the reset button, unplug the unit and hold reset for another 30 seconds
• Plug the unit back in STILL holding the reset button a final 30 seconds

I downgraded back to stock WRT54GSv3_4.71.4.001_fw did the 30/30/30 again then upgraded to dd-wrt.v24_mini_generic however I found it didn't had support for SD cards in it which is a future mod I have planned so again I did a 30/30/30 and downgraded back to stock before reupgrading to dd-wrt.v24_std_generic

One of the first things I did was enable SSHD via the 'services' tab however when I clicked apply setting my browser was forwarded to a blank white screen @ http://192.168.1.1/applyuser.cgi I tried the same again in a different browser and it worked fine, it may have been a remnants of an old session cookie or something.