Fire up your KDE Control Center. If there's no mention of KDE's version number, then it must be 1.0.
Another clear difference is the 'K' on the panel. In 1.0 it's a black-and-white 3D K, while in 1.1 it's a white K on top of a wheel.
Or if you have installed KDE from RPMs try:
$ rpm -qa | grep kde kdesupport-1.1pre2-2rh5x kdeadmin-1.1pre2-1rh5x kdelibs-1.1pre2-1rh5x kdegraphics-1.1pre2-1rh5x kdemultimedia-1.1pre2-1rh5x kdetoys-1.1pre2-1rh5x kdegames-1.1pre2-1rh5x kdeutils-1.1pre2-1rh5x kdebase-1.1pre2-1rh5x |