When installing a Series 60 theme and you get an error message saying
"Series 60 Scaleable Skin Support Reuqired"

this means your handset is not a Series 60 3rd edition model and does not support the theme you are trying to install.
Series 60 Scaleable Skin Support cannot be installed into your handset either.

Here is a list of models supporting this feature:
Nokia E50, E55, E61
Nokia 5500
Nokia *N70, N71, N72, N73, N80, *N90, N92, N93

*note - N70, N72 and N90 are NOT s60 3rd edition models, but still support the feature, they are an exception.