Given your heavy cross-platform emphasis, I would consider writng my own installer (this is a project I've been half-considering for a while). I found MakeMaker less than ideal for installing binaries (while being brilliant at installing modules).

You should look through the File:: series of modules to give yourself a chance at cross-platform compatibility.

Also consider using one of the free 'InstallShield' clones to package your windows version.

And to make life easier for anyone who's packaging it, make sure you keep all your install variables in one easily accessable place.

Having said all that, your planned locations sound fine, that's the sort of thing that I do with mine. It works, but people are likely to have opinions on the correctness and efficiency of that approach.

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Jeremy
I didn't believe in evil until I dated it.