Hi,
Now that we have the Forcefield Editor inside MS 4.3, one can start using 'old' forcefields from Cerius2. Only the 'dreiding-like' FF are supported in this release but still one can use the (world famous!) cvff-aug or the Watanabe_Austin forcefields.
I put a rather long list of all the one I could find that works in MS 4.3 in attachement.

Best
Marc