Starfleet Jedi

All of the Minbari ships and fighters are replaced by Imperial capital ships and fighters (SW) at the Battle of the Line in Babylon 5. Admiral Piett will be in charge of the fleet, though his flagship will be a standard Imperial Star Destroyer. Also note that the Star Destroyers get their full Imperial fighter complement. What happens? Does Earth manage to stop them, or is Earth still doomed especially since the Imperials don't care much about human souls and their attributes?

I think this is a curb-stomp in the Imperial's side. Just by sheer weight of numbers, Earth basically being on its last legs by this point, and B5 not being one of those "crazy supertech firepower" universes unless you're a First One. Though Earth will probably inflict a lot more casualties on the Empire's fightercraft.

It helps that from what I remember, artificial gravity is usually a measure of advanced technology in the B5-verse, and the Empire has that in spades.

Well, that really depends on what this scenario translates into.
For a measure of comparison, my recent appreciation of the overall advancement of Star Wars tech has it brought down by a few notches, so much that any group with a technology that provides space faring, armour, laser/nuke/KEW in the low kiloton range has more than a fair chance against the bog standard ISD.
Earth may not have a widespread use of artificial gravity, but it's only a given piece of tech that doesn't mean much in battles. It doesn't prevent railguns or coilguns from operating, nor does it stop plasma guns or laser cannons either. Not to say anything of missiles.
Even the most impressive elements about Star Wars, like shielded fighters that can survive a couple shots that would probably utterly pulverize a modern Abrams, aren't even on the Imperial side since they seem to rely on rather weird fighters (stoopid solar panels which make sighting a problem), which for all we know now, don't even come equipped with shields either.

So what are the forces on each sides exactly?

Well, the Earth forces get their capital ships and Star Furies that they usually have, plus any nukes that they may have available to them since this is expected to be their last stand. The Imperials get their full complement of fighters, TIE Fighters, TIE Bombers, and TIE Interceptors as seen in the movies. Simply replace all of the Minbari ships with Imperial Star Destroyers, since those are the only Imperial capital ships that we really know about. As for fighter numbers, until we get more information, I'll allow the EU fighter complements of the ISDs, but only for the TIEs since we don't know if any of the other support craft besides those Lambda-class shuttles, which appear to be transports rather than attack craft, are still present.

Ok thaks. Now what is the fleet composition on each side? Does Earth use defense platforms? What are the total numbers we shall use, roughly?
Are there some mitigating parameters?

All I know is that there were 20,000 ships/defenders at the Battle of the Line. I am almost certain that this includes fighters, support ships, as well as capital ships and I don't know the breakdown of the ships. I also don't have the Minbari, now Imperial, numbers for the battle.

Enterprise E wrote:All of the Minbari ships and fighters are replaced by Imperial capital ships and fighters (SW) at the Battle of the Line in Babylon 5. Admiral Piett will be in charge of the fleet, though his flagship will be a standard Imperial Star Destroyer. Also note that the Star Destroyers get their full Imperial fighter complement. What happens? Does Earth manage to stop them, or is Earth still doomed especially since the Imperials don't care much about human souls and their attributes?

1) I'm going to assume equal levels of firepower.

2) The human fleet as I recall was any armed ship, and that star fury were likely counted as if that were starships.

Fighter on fighter combat
Star Fury pilots aren't normally depicted as very good:
Straight and level 1
http://www.youtube.com/watch?v=S4nOHCeL9H8
Straight and level 2
http://www.youtube.com/watch?v=jez-dpR_vsk
straight and level 3
http://www.youtube.com/watch?v=oOcmdUGfeug
This sort of thing got rebel pilots killed at Yavin

Now the battle of Endor
http://www.youtube.com/watch?v=xPZigWFyK2o

I'm going to give this to the Empire.

Even with equal firepower the Empire still has an advantage in shields, and that the first 2 thirds or 3 fourths seem to be expendable storage and airfield. I wouldn't be all that suprised if the Empire could win by ramming the E.A. forces.

On the starfighter side, the Empire would have the clear upper hand. And since the B5 ships are not immune to the firepower of small crafts, they'd get in serious trouble as soon as Imperial crafts would pass the first waves of Star Furies.