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.

One of the header fields given by the client for HTTP 1.1 is:

Content-Range: bytes=<start>-[end]

Edit: For more information about server side stuff, check section 14.16 in RFC2616.
Edit: here's some information about client side: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35