Did you know that you can lose the mission Siege and the campaign continues? To all those who are "giving up on the campaign because of this mission", just skip it and move on. Once you get better at the game you can revisit this mission and try again.
I beat the map on normal difficulty, and I didn't fight the Yor or the Dread Lords once. I simply purchased all of my ships/buildings fast (you better use that 30,000 quick) and colonized towards the SW corner of the map. I made no factories at all, and spent all of my money on research and labs, gaining tech as fast as possible. Finally establishing a Starbase at the forward planet, I pumped out transports and headed for the target planet. By this time I'd researched almost every invasion tech. We took them down with Orbital Bombardment. Don't fret, it's possible. Just stay focused on the objective.
