Will the LXDE 1-click install yast package for SuSE 11.0 work without any problems with 11.1? Or would I be better off installing it from source?
Add the 11.0 repo and try it that way. If it need loads of dependencies it could be a problem. You would want to install the 11.1 of any dependencies. That way you just end up with LXDE being the only package you install from 11.0 and so removal will be easier.
You could download the .rpm from the 11.0 repo too and install with that, which should be fine if there is not a list of dependencies.