You should always refer to the Compatibility Matrix: Cisco Unity, the Cisco Unity-CM TSP, and Cisco CallManager at:
http://www.cisco.com/univercd/cc/td/doc/product/voice/c_unity/cmptblty/tspmtrx.htm
That being said there is a defect with TSP 6.0(2)a that will not allow it to install on NT 4.
You can wait until 6.0(2)b is posted to CCO (in the next day or so) or install 6.0(2). The only difftrence between 6.0(2) and 6.0(2)a is that 6.0(2)a fixed a problem with the TSP install for W2K SP3.