I haven't worked with Aptana in a long time, but I've used Eclipse quite a bit, and I believe the tab-switching is bound to Ctrl+PgUp (or PgDown) by default. I just recently installed Galileo, and used this as an opportunity to try rebinding to Ctrl+Tab, but didn't have any luck.
I know I got this to work on previous versions of Eclipse (at least Europa, and possibly Ganymede), but am not certain why it's not working in Galileo. Regardless, here's how to find the key-bindings in an Eclipse install (I would assume Aptana uses these bindings as well):
Windows->Preferences->General->Keys
From there you can try filtering the key-binding you're looking for (e.g. "tabs" or something) and input whatever combo you want.
I would also recommend searching for the key-combo you're going to use to make sure it's not already in use. If it is, you'll want to re-bind the conflicting binding, so they don't collide.
Have you tried CTRL + E ? – ukanth – 2009-12-08T09:50:10.603