I'm not really that good with excel but I've created a spreadsheet that will give you three graphs for any finish distribution you supply (up to 18 placed itm finishes), for any amount of games, and any buyin.
(i) the Normal (bell curve)
(ii) CDF, cumulative so you can see what % of time you earn less than x.
(iii) an envelope, showing the max-min spread for the (1% & 99%), and (10% & 90%) levels
Here is an image of them
TourieSpread.xls
just click on the "Download: TourneySpread...." at top of link page
On the sheet you can/should modify any of the non-grayed areas, I was going to 'protect' the sheet but then you can't re-size or move the diagrams - if you want to just go to 'Tools | Protection" and select protect sheet. I have made two sheets - at the moment the first is an STT, the second an 18 seat but you can change these.