I know a a little of star wars... their tech i'm kind of familiar with, less so with their factions admittadly.
I think that the "dark side" would side with no one, settling only for conquest (i have seen all the movies). The republic and rebels would side with the Federation and it's allies as it's motives are almost the same.
However, getting into the weaponry, for the MOST PART, the standard battle weaponry seems relatively inferior to anything in the Federation. Yes there is the deathstar, but that thing seems to be relatively stationary and slow. The federation would detect that thing lightyears away and send a force to destroy it.
From what I've seen, all factions seem to use lasers, or some form of laser. I've heard star wars fans claim incredible power outputs for their weapons, but i've never seen any hard proof other than the large planetary weapons such as the death star. And as far as physics go, a laser is a laser is a laser. You could add some kind of particle component to it i suppose, but it's still light amplification technology at its base, and that technology has LONG since been antiquated by anything Starfleet as to offer.
Their sheilds seem realatively weak too...
http://www.trekbbs.com/newreply.php?do=newreply&noquote=1&p=2651265 .... this site goes into more canonical references than I could however.
As far as tactical systems go, I haven't really seen any hard numbers for outputs of their beam weapons, missiles, or bombs, only inconsistant evidence. Again visit that site.
The fighter shuttles too seem to have no shields whatsoever, which to me would be easy pickens for Starfleet and it's allies. Phaser and disrupter arrays seem to be able to multi-target, easily picking off those silly fighters at will. Also, in Star Wars, it seems that they still rely on turrets, another technology that has been antiquated by Starfleet with the much more versatile arrays. Take a turret out it ceases to function. Take an array emitter out, the second back up still fucntions as does the rest of the linked array.
Also, unlike Starfleet, the main ships aren't usually the ones in main battle, and they are large...VERY large. A Federation ship could run circles around it punching small holes here and there around critical systems....death by a thousand cuts so to speak.
For these reasons I believe that the republic would side with the Federation...sheilds not withstanding, they now have armor generators and ablative armor as well.
However, the one thing that the "Dark Side" does have above any Federatioin ally is numbers...they have the ability to swarm like ants....this would post a signifigant problem if they invaded as Starfleet can't be everywhere. It seems they might have to consolidate their worlds a bit or risk occupation. Howsever, a ship could simply go to an invaded world and beam the invaders off the planet as soon as they've destroyed the enemy vessel, which from what i've seen would be relatively easy.
http://www.trekbbs.com/newreply.php?do=newreply&noquote=1&p=2651265
go to that site it's pretty decent and bi-partisan..