On the Area forums, a customer reported that Softimage memory usage would keep increasing until the software either froze or crashed. All he had to do was keep moving points. This happened both on Windows 7 and Vista.

Eventually he resolved the problem by rolling back to an older version (June 09) of the display driver for his [uncertified] ATi Radeon HD 4870 card.

Ref: XSI crashing / freezing within Windows 7 x64