Scene Size: The file size would probably only be that large if everything still has it's modeling history intact. You'll want to select anything static and hit the Freeze button (lower right corner, under Edit). For anything that is weighted to a rig, you'll want to hit the FreezeM button in order to keep the envelope…
Usually when you compress 3d files using a zip archive or similar compression you get pretty huge size reductions. I just zipped a maya file and it was roughly 1/4 of the original size. Also, I don't know the equivalent in XSI, but running the Optimize tool in Maya will delete a lot of extra nodes and stuff that will save…