Can I retrieve the position of an offline player in SMP?
Solution 1:
Yes. Use NBTedit or its successor, NBTExplorer.
Download and run it, choose File → Open, go to your Minecraft server directory, find players directory, and then select the name of player you want, for example Player.dat.
You should see something like this:
You need to go to "Pos", and there you have it, coords of player you wanted.
Just double click any to edit it.