Have you heard about an NT/2000 emulator for Sun Solaris? The goal is be to run the Windows Applications within such an emulator on a Solaris OS.
Do you like wine? I know I do. This is almost as good as the stuff you drink, from Wine Development. Look at the info on this url http://www.winehq.com/. It supports Solaris. It also supports Linux.
If you need to run run Windows and Unix on the same box, but not at the same time, you may also want to think about using a PC and having seperate Windows and Solaris (Intel version) partitions.
This was first published in May 2002