Yes, that's exactly what the texture loading functionality is used for. This is the general process: http://www.mksecrets.net/forums/eng/viewtopic.php?f=65&t=5188
The tutorial is a bit old (I just googled and picked something), so ignore what it says about 3.0 and newer versions, and go to C:\Users\<username>\Documents\Dolphin Emulator\ when it tells you to go to the User folder.
You should by the way update to a recent development build or 5.0 release candidate. If you do this in 4.0.2, any textures you dump will be in the old format, not the new improved one.
The tutorial is a bit old (I just googled and picked something), so ignore what it says about 3.0 and newer versions, and go to C:\Users\<username>\Documents\Dolphin Emulator\ when it tells you to go to the User folder.
You should by the way update to a recent development build or 5.0 release candidate. If you do this in 4.0.2, any textures you dump will be in the old format, not the new improved one.