Hey Guzman
Try using Syflex plugin instead (included in XSI) the documentation is in the install folder > Doc > Syflex
It is a far better cloth simulation, and has higher computation.
Check out Digital Tutors 'Syflex for MAYA' to get a good idea of the scale and use, most of the video tutorials apply to XSI too.
Post back here if you have a problem..
D