With the WRT150N it is important to first flash the mini image and then after dd-wrt works you can flash the standard image!
Do not use micro and mega images, as these may brick the router...
After flashing it is possible that the WebInterface is not enabled!
To enable it, connect to the router via telnet (Port 22) and use following username: root and password: admin
You can then simply start the webserver using:
httpd -h /www
And connect to http://192.168.1.1 via a browser if the router is directly connected to the computer.
To change password for the root account on DD-WRT use the simple command:
setuserpasswd <user> <passwd>
It is highly recommended to reset the router to factory defaults after flashing, since otherwise there will be errors quite certainly.
More tips to follow soon!