I may repeat several already made points, and dispute a few others. If you don’t like it, to fragging bad, write a response and deal with the pain.
OK, it boils down to a simple matter of policy:
Enterprise Contact Policy:
Step 1.Hi we’re the federation. Will you be our friend?
Step 2.Hello Why aren’t you answering?
Step 3.<continue on with similar inane drivel until they finally leave>
Galactic Empire Contact Policy:
Step 1. Surrender NOW.
Step 2. <Open Fire Subcommander. Blast them into Muons>
As for the reasoning that the enterprise could simply beam over a few photorps into the ISD, because since their shields wouldn’t be designed to stop transporters, utter nonsense. Firstly, they’d have to think of it, and aside from Scotty, the average cunning of a starfleet officer appears to be on the same order as a rather demented goldfish. Plus theer is no reason to think that transporters wouldn’t be stopped by Imperial Ray/Particle shielding. They stop Turbolasers, Ion Cannons, and small warheads, so Transporters would probably not be a problem.
But assume that for some reason you were able to beam a party over to the ISD. Imagine Heavily Armored, Armed, Imperial Storm Troopers vs. Pajama Wearing, Flashlight Wielding, Starfleet Yellow-Shirts. Personally I know who MY money is on. ISD’s Carry THOUSANDS of troopers. Transporters can beam 6 at a time. And for those of you about to mention the first Death Star, it was the size of a small moon, and that is alot of volume to cover even for 100,000 troops, much less a reduced garrison.
A friend of mine (who shall remain nameless) Suggested that if Scotty were there, he would do the same thing he did on the Kobiashi Maru scenario. FOr those of you who don’t know, Scotty scored teh highest Legitimate score on the KM test in starfleet history. He ALMOST beat it by beaming Anti-Matter canisters into the seams of the enemy vessel’s shields, then beamed back just the canisters. This had a very detrimental effect on the enemy vessel. ISDs, being rather more heavily armored than anything in the ST universe, would take this ploy, shrug off the damage and lay teh smack down on whoever was arrogant enough to think it would work. This isn’t to say they wouldn’t feel it. They would take damage, and have to make quite a few repairs. It is to point out the difference between a properly designed warship and a family camper(i.e. the 1701-D/E).
As for the matter of laser blasts being ineffective against the Enterprise shields, that is blindly optimistic at best. as mentioned, they were refering to LOW power lasers. To clarify this for all the dedicated Trek-heads out there, I will draw a nice, clear, modern example for you:
There is a reason the Iowa Class Battleship wasn’t retired until after the Gulf war. the Low power laser refered to in the quote mentioned would be, on the scale we are talking about, be equivalent to about a .50 cal heavy machine gun. Good enough for small targets such as trucks, tanks etc, but a peashooter against an armored fortification. A turbolaser would be about equivalent to Big Mo’s 18 inch bombardment guns. i.e. armor/shields? what armor/shields? ISDs also, ton for ton, pack more guns than a redneck NRA chapter.
As for the question of Empire versus borg… Empire, partially because of above reasoning, partially because they don’t try to assimilate anything. They crush it under-boot.
I COULD go into several other points, such as fighters, Sith powers, FTL combat (impossible ), Social Differences (aside from wearing spray on dresses/uniforms, just what IS the point of a ship’s councelor?), etc, but it is late and I’ve given you all quite a bit to think about already. 
Love, Luck, and Lemmings to you all 