Well if you already have XSI that's for sure another story !
XSI is a great product, even in its foundation edition and at a price !!!
Too bad it doesn't exist on Mac...
(natively, you can always run it
via Bootcamp or VmWare...)
Anyway, as i said if you ever want to buy it, just tell me and i'm sure Newtek Europe can get that sorted out !
Cheers,
Laurent aka Tartiflette