Hi,
according to the feature navigator the Catalyst 4500 does not support MPLS. The Catalyst 6500 supports MPLS, MPLS L3VPNs and much more through either the OSM module or with the Sup720.
Infact there are numerous enterprise implementations of MPLS L3VPNs based on the Cat6500 being PE and "CE switch" in one box.
In case you are looking for Multi-VRF functionality the Cat4500 can do it. So it can be a "PE extension" in your network. You can implement different VRFs on it (control plane) and forward data separated by dot1Q headers (data plane) to get a "clean" separation including IP routing on the Cat4500.
Hope this helps
Martin