a) Contact one of the developers by visiting http://negafinity.com
b) Post a question on the HaloCraft 2.0 forums by visiting http://halocraft.us
Type in the modpack name (HaloCraft 2.0) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select HaloCraft 2.0 from the list on the left. The launcher will handle everything else!