Hi all,
Im a middle of the rd backpacker, and i'm thinking of going to mexico in mid january, could you please tell me about the weather at that time of the year before i make any plans. thank you all. MARK

Mexico is large and the weather varies greatly by region. I suggest that you go to Wunderground and click on the Mexico list and look for yourself by history and area where you might be considering.
as mayaphile says go to her link on mexico weather underground, pick a location, and then from there you can also scroll down to history and almanac and then pick the month of your travel and 06,05, etc. from there you can get the temps, rain.etc for a week, month etc. for the cities and thus get some idea of what the weather might be like.