Photoshop: how can I access other directories beside DCIM?
Asssuming you mean Adobe Photoshop Express it is set by default to only show you Camera pictures. You should be able to change a setting to make it look at the rest of your phone's storage.

Open Photoshop Express, press Menu (on ICS press the ... in the corner of the screen), select More and then Settings and scroll down to near the bottom where you should see the option Show camera photos only in Phone view, take the tick out of the box and press Back to get back to the main Photoshop Express window where you should already see it filling up with all the pictures it can find.