you can use the latest version of the dedicated server (1.07.615) and with a small modification you can allow any client of any version to join it or just only those of 1.06.
In attachment you can find a quick patch that must be applied with lpatch:
http://aluigi.org/mytoolz.htm#lpatch
launch lpatch.exe, select halover.lpatch, select haloded.exe and you will see a such message.
then launch the server and try to join it with your old 1.06 client, it should work.
the alternative method is setting the 1.06 version (or any other) instead of 1.07 and is probably better (I can post quick lpatch files for this, just ask).
anyway as far as I know version 1.06 uses the same version of 1.07 (612000) so the clients of this old version can join the 1.07 version by default... except in the case you want just to use the 1.06 server version in which case I can't help.
