By popular request I am putting the Mk1 Omnimech pages back up on the site - Slightly redone using Heavymetal Pro to make them legal for level two play. I've made .PDF's of the record sheets from HMP so lacking access to the official software are not left out in the cold.
The Software section will hopefully be filled up with the various free/shareware programs available for Classic Battletech. This probably won't be a complete archive for some time, so in the meanwhile I highly suggest you check out Pryde Rock Industries which has a fairly extensive archive with full info on the various programs that are out there.