Yeah, the dreadlords can be tricky.  One thing you have to keep in mind is that you will lose a lot of ships in the beginning before your tech gets high enough that you can start turning the tide.  I didn't even bother with setting up starbases, except for the ones they give you, since they would just get destroyed.  By the time I was powerful enough to defend them, there really was little need to even build them.

In the beginning, just try to keep your planets defended so that they can't bring in the troop support to take them over.  If the opportunity presents itself, take out one of their ships...  Remember that the AI is not the most intelligent and, rather than sticking around until their troop transports arrive, will move their fleets to another location and the transport will come in later, undefended.  So, after they eliminate your defenders and have moved elsewhere (which they do right away), make sure that you have another defender built there.

Make sure that a lot of your focus is in developing stronger weapons and logistics.  And I'll second that on the defense - they are useless against the dreadlords.  Once your weapons and logistics are high enough, you will be able to make groups of either small ships, as dmantione suggested, or use medium sized and small ships combined, which was the way I went.  Once you can start getting high enough attacks, you'll be able to start taking out on their ships for each one that you lose... once you get there, you'll have no problem with them.

I find that they use the Doom ray a lot more than any other weapon so if you want a defence use beam weapon defences. Also make sure you attack first when engaging and attack in fleets of about 4-5 fighters. That will handle most the smaller vessel's. The largervessels may be a problem though but I find that if you have a military starbase in the area it will become much easier to kill them. Use small ships, keep them in large fleets and always engage first.

That's what i normally do. Good luck.