Can I have a write permission in android Read-only file system?

Whenever I try to update framework-res.apk on system/framework folder on my G1 it gives me an error:

failed to copy 'framework-res.apk' to '/system/framework/framework-res.apk': Read-only fil开发者_如何学编程e system

Then I tried to mount it with read write permission with this line:

mount -o remount,rw -t yaffs2 /dev/block/mtdblock3

But it says Usage: mount [-r] [-w] [-o options] [-t type] device directory

And I read on forum that you have to access with su command But whenever I try to hit command su it says permission denied.

try visionary for rooting your phone (http://android.modaco.com/content/software/320350/19-nov-r14-visionary-one-click-root/) and then su would work for you.