When you get a Softimage 2010 network license, you can use that license to run XSI.exe or xsibatch.exe on either Windows or Linux.
Softimage 7.5 licenses were not cross-platform, because we used FLEXnet licensing on Windows, and SPM licensing on Linux. But as of 2010, the Linux version now uses FLEXnet licensing too.
See the press release for Softimage 2010 pricing.
Note that the specified prices (SRP and upgrade) for Softimage 2010 Windows are for a standalone licenses. Network licenses are more expensive than standalone licenses.
Also, Linux licenses are always network licenses. That is why the press release shows a price difference between Softimage 2010 Windows and Linux: the Windows price is for a standalone license, and the Linux price is for a network license.
Softimage Advanced licenses are always network licenses (since Advanced includes Batch licenses, you need floating licenses to be able to use your Batch licenses on render nodes).