roxio jam (with toast) can do it easily..
you can of course, do it yourself with a bit of extra work in sound studio. (this would probably work in peak if it has similar functions)
open up the 2 files you want to mix together
fade out the end of file 1
fade in the start of file 2
find a point towards the end of file 1 where you wish to begin the crossfade
select from this point to the end of the file
cut the selection
in file 2 go to the very start of the file and go to edit > "paste mixing"
kind of a convoluted way to do it, but it works..
-Mark