All sounds good.. tend to use the older dd-wrt firmware to do this.. 2.4 linux kernel is far more successful than later 2.6 versions of dd-wrt.
You must manually setup wireless.. plainly only 2.4ghz is going to work.
So jump into the airport utility manual setup.. and go to the wireless page.
Depending on how old your TC is, setup a wireless name.. no spaces no special characters.. very short also is just as useful as very long. tc24 will do nicely.. Change the name of the 5ghz if it is later model to something also similarly simple.. tc5 might be nice. Call the TC a nice name again no spaces.. which it will have by default.. no special characters pure alphanumeric. TC is nice simple name.. Hard to forget really.
Set manual channels for the 2.4ghz.. this is utterly important.. repeater or bridge does not work with auto bouncing all around the place. Choose a suitable channel out of 1, 6, 11.
5ghz won't matter so you can leave that on auto if you want.
Lastly security..
Let me suggest to start leave security off. Get it setup so you know it works then come back and test the security levels.
I am not sure what to select here.. you want wpa but the dd-wrt says not wpa+wpa2..and apple do not offer straight wpa as the bridge cannot resolve which to use.. you might need to use wpa2.. but that doesn't work on some routers with repeater.. or bridge.. you are going to have a bit of trial and error here.
Make the password something nice.. you guessed it pure alphanumeric.. no spaces, no special characters.
be creative and simple.. tc24passkeynot5 .. of course use what you like.. I am giving examples to make it easier. Update the TC.
Now just do the bridge setup on the WRT300.. there are two kinds of bridge.. client bridge and wireless bridge.. there is also repeater. Client bridge has no routing .. that is what you want. But it does other things which may make you go back. Please note bridges are strange beasts.. this is going to hide clients behind the Linksys MAC address.. and it can lead to issues.
Anyway read the setup tutorial. http://www.dd-wrt.com/wiki/index.php/Client_Bridged
You will find earlier one if you use the index.. this is also useful to read. And is more extensive.
http://www.dd-wrt.com/wiki/index.php/Wireless_Bridge
There are several scattered around and I can point you to others.
When you are finished you will often need to reboot both boxes to get the bridge to establish.
Once you are done. See how it goes..
I tend to advise people that wireless bridges are flakey and will do down at the moment you want them to work. You can get EOP adapters which tend to be more reliable and use the WRT300n in wan bypass as a switch and WAP.. This is much more reliable.
