OK, specifically I used the HTC media player, BTW. From there, just start playing any song/sound you want to trim and press menu->Set as Ringtone. From there you can either set it unmodified as your phones ringtone, assign it as a contacts ringtone or trim it. If you trim it, it gives you 2 sliders to move to set the start and end.
Once set, it goes into the /Ringtones/ folder in your SD card.
To drag in your own Alarms, Notifications, and Ringtones create an MP3 folder in your SD card. Then, add "alarms" "notifications" and "ringtones" as folders inside there. Now, you can fill these up with files ( and even more folders for some organization, though you won't see the folders when setting them from the phone. )
So, you can use the HTC media player to trim any playable sound and save it. Open it up from the /Ringtones/ folder and move it, or copy/paste it into any/all of the /MP3/alarms ; /MP3/notifications and /MP3/ringtones folder so you can easily select them from within the phone
PS: I can't take credit for any of this. Someone else posted here in the forums some time ago, I'm just reposting in my own words because I have no clue where that post was, lol.