I thought Mothership Zeta was solid awsome, but i couldnt help but notic that the ship that you destroy in the end slow drifts to earth, wouldnt that give people the alien tech?
Depends. The ship will begin to accelerate as it's orbit deteriorates. The ship we destroy had major hull breeches, exposing numerous decks. Depending on various factors (ship design, whether or not any propulsion components are still enabled, etc.) the ship will probably be severely damaged by re-entry. Due to the extent of the damage, it may break up in the atmosphere. If a big enough, not gutted piece of the ship survives to hit the ground, then the various factors of the landing will determine how much of the wreckage is just scrap metal. Any computer software would be the least likely, if ever, to be adapted by anyone who found the site. Both because of the limitations of the setting, and that aliens may use a programming language that makes no sense to us and uses an entirely different set of symbols, which, except for numerals, most likely don't have any real association with our symbols. [in terms of, a particular symbol isn't just the english alphabet in a different font (I'm looking at you, daedric), but represents something entirely different.]
Chances are, that any deep space ships like the saucers we see would have fabrication centers, but considering the level of damage those are also very likely to be destroyed. Any technology that is salvaged would most likely be used for a time then discarded, and very few bits could eventually make their way into the Brotherhood's hands, or the commonwealth's Institute, etc. But I doubt they'd get enough to re-write their group's tech level. Honestly, the best hope for technological revolution is in Zeta itself, since much more of it is intact.
As for the aliens, who knows. Realistically, those aliens were on a deep space exploratory mission. Chances are, they were the only members of their species within light years of Earth. I doubt the aliens would bother to go looking for them, they will instead probably just write it off as the dangers of space exploration. Or maybe send a probe. My own guess is that they wouldn't' actually send another ship until they were sure they knew where their lost ships were. And even then, when there are so many other star systems in the galaxy, their is no real motivation for them to bother with Earth after the loss of two ships of such size and cost.