CITRIX isn't a Window Manager.
It looks like Gnome2 is the default WM for RHEL 5.8 but I can't find anything that explicitly states that.
System -> Preferences -> Keyboard shortcuts
Set the shortcut for Move between windows, using a popup window (default is
Alt+Tab). It's possible you are using
Compiz or another WM though, so figure that out.
However, noticed you mentioned
konsole, the official KDE terminal emulator. This suggests you may be using
KDE. To switch tabs in
konsole the default is Shift+RightArrow or change it
Settings -> Configure shortcuts -> Next Tab.
To switch windows in KDE
Alt+Tab or change it
System Settings -> Window Behavior -> Task Switcher -> All windows