[russell]

Absolutely the first thing to do id you want to pursue this is to get rights to the software from the bank. In the US they own it because you were an employee using their resources. Use a lawyer because employment and IP law are a mine field. (Oh, you are a lawyer. IANAL, but my advice is still good. :-)

PG mentions a web based service which I think is the way to go, but some kind of Excel add on might be easier to sell. If it is web based, look at the fog creek model because adoption is cheap and painless.

As far as University vs startup, some great companies have been founded in grad school.

I say go for it. Scratching your own itch is a good motivation for producing a goo product, particularly since it is in a domain little served by HNers.