Urgently need English Grammar detection/correction software!?

I really hope someone can help me out. Basically, I can write just fine. I have a friend, getting his masters of philosophy in Ukraine. Well, he has enlisted my journalistic skills in helping him to finalize a tourism type guide translation from Ukrainian to English. He wrote the entire thing originally and I'm sure it makes perfect grammatical sense in his language but when he used one of the translation tools it did alright. Maybe 95%. For example, it may put the word "of" instead of "on".....just an example. So, I am left with 20+ pages of this minor changes to help polish it off, but I have noticed that when I change the few words that didn't cross over quite right it changes the flow of the sentence. Long story short I am ending up having to almost rewrite the entire thing, saying the same thing as the translation but I'm having to move, change, and switch so it all is darn near perfect. So, PLEASE tell me of any kind of software, freeware, a simple checker, something to make it where I do not have to manually do this. I will be so much in your debt! Thanks! Due Thursday, Ukraine time.....so, by 1am here. Thanks for any help, sites....anything!