I don't know about Schism, but the sample editor in Impulse Tracker is one of my major complaints with it. It's not actually very good, since all you've got is a very small, very pixelated visual marked by your loop points. The only way to crop or trim is to turn the looping on, set your loop points to contain everything you want to keep, and use the Ctrl+B and Ctrl+L commands to cut the sample before the loop and after, respectively...icky.
Most of the modern trackers I've looked at feature much better sample editing interfaces (at the very least they give you a much larger visual of your waveform). Strong examples would be MadTracker, ModPlug (I hate what they did to the keyboard layout in Open ModPlug), and Renoise.
My personal favorite 'tracker' is Buzz, followed very closely by Impulse Tracker 2.14 (all time best tracker ever

), but Buzz is a beast to learn and there's not much in the way of sample editing and a 50/50 keyboard and mouse interface. Most newer trackers will unfortunately make greater use of the mouse than the pre-Win32 ones, but I'm pretty sure all of them at the very least have keyboard shortcuts for the most important commands. Both MadTracker and Renoise have the keyboard shortcuts listed in their respective help files. Just use a cheat-sheet

Old dogs like me just have more trouble learning the new tricks, cheat-sheet or no
