Like mattrix said, the Android image is already rooted, though some tools still need to be told to use root access since they have it disabled by default as a safety precaution. One of the best tools of this kind is "ES File Explorer" where you can simply change the parameter "Root Explorer" from its default "OFF" value to the "ON" value which enables read-write access to the root folders.|
As for the issue with /sdcard mounting, I solved this problem for my own use earlier today, and have written a simple tutorial for others who may want to do it the same way. Doing so is extremely simple, as it only involves changing a single bit in a single file (changing a "2" character into "0"), for which you can use the "ES Note Editor" which is included with the "ES File Explorer".
The file affected by my change is "/etc/vold.fstab".
You can read all about it in the separate thread where I posted that tutorial.
Best regards: dlanor