Sun has recently started several projects to aid in the transition.
Their WWW starting point is:
Solaris Migration Initiative home page
The project is a combination of new and existing efforts and includes:
1) Porting PD software to Solaris 2.x
2) Solaris Migration Tool: (formerly known as Pipeline tool) a tool
to help you port your code.
3) Admigration Toolset. Tools to help you convert your SunOS 4
environment and to help you adjust to the new Solaris 2.x environment.
4) Appmap: a tool to simplify application administration in a mixed
SunOS 4.x/Solaris 2.x environment
5) Solaris Transition CD
6) Native Solaris NIS
7) LP tools (simplified LP administration through NIS)