This lets winamp seek to a specific place in the file (IE, the user dragging the seek bar) and start from there. Without this, the server would just send the whole file again

Well, my app is currently restarting the song when you try to seek, and I'd like to fix that, but I don't know how. That's really what I was asking. In Winamp, I seek to a point in the middle of a song served by Hijack, works great. I try to do this with a song coming from my server, it doesn't work so great. I don't know where this is fixed.