You have problems with spacing around punctuation, and you have spurious double spaces in a number of places. I have corrected these below.
The other changes that I made to the date formats are not because what you had was wrong, but just to make them all consistent.
Dear colleagues,
This year the company is to organize a vacation trip for all employees to Mui Ne Beach, about 200 km away ["away" is not necessarily wrong, but I think the sentence reads better without it] from the city center. Those who would like to join the trip should register with Miss Perry by February 15, 2008.
The trip is scheduled to leave for Mui Ne Beach [comma deleted] on July 15, 2008 and come back return ["come back" is not wrong, but I think "return" is better] to the city on March 5, 2008. [The return date is earlier than the departure date!]
Thank you in advance.