I agree with Aldo (and most everyone else); Beams for a pre-FS2 game are a BAD idea.
It's implicitly stated in FS2 (maybe in the tech database?) that the GTA and the PVN didn't even concieve of beam weaponry until the SD Lucifer (with its flux/beam cannons) was encountered in 2335. It took the GTVA several more years to get the design of beam cannons right. In fact, when beam cannons were first installed on some of the older Vasudan Typhon destroyers, they caused engine overloads and power failures on these ships. New ship classes (like the Sobek corvette and the Mentu cruiser) had to be designed just to be able to use these new beam weapons without malfunctioning or endangering the ships.
In light of that, making any sort of beam weaponry before the GTVA managed to design them in the years leading up to FS2 would be going COMPLETELY against FS canon.
And LtNarol, as for your comment that "that said nothing of beams _before_ the Great War, just that they didn't have them _in_ the Great War," you have to remember that the T-V War (which led directly into the Great War) lasted for 14 years. Before that time when the Terrans encountered the Vasudans at the start of the T-V War, the Terrans hadn't even encountered ANY space-faring life and would have had no need to mount weapons on their ships. Thus, the only time the Terrans could have downgraded their weapons would have been DURING the T-V War, which makes no sense. What kind of military downgrades its weapons during wartime? That's suicidal and completely against all logic and common sense.
Ummm, beam cannons before FS2 are bad, so don't put beam cannons in a pre-FS2 campaign, mmmkay?