Note: These notes were created some time ago and were in the Rhino Help. But it seems that people who know about this subject should review and update this information, so I'm moving it here. ~mb
There are two options for getting NURBS models from Rhino into Softimage. Both have their own problems and benefits.
Softimage can also import 3DS, DXF, and OBJ file formats created in Rhino.
iges2soft -f -L -S3 -s3 -T5 -t3 -v3 -R [RSRC_DIR] MyIgesFile.igs MyDSCFile.dsc
[RSRC_DIR] = Softimage resource directory (often c\soft3d_3.7\3d\bin\rsrc)
iges2soft.txt contains command line option information.
Polytrans by Okino can read IGES files and write Softimage files. Check out their web site for more information: www.okino.com.