Leap year calculator
Logic

Consider the if condition, which I have reproduced below with different alignment for ease of viewing…

if (year%4==0 and year%100==0 and year%400==0)or \
   (year%4==0 and year%100!=0 and year%400==0)or \
   (year%4==0 and year%100!=0 and year%400!=0):
    …


It's clear that the first two lines can be collapsed due to redundancy.  As for the third line, any number that is not divisible by 100 is automatically not divisible by 400 as well.

if (year%4==0 and year%400==0)or \
   (year%4==0 and year%100!=0):
    …


That can be further simplified to:

if (year%4==0 and (year%100!=0 or year%400==0)):
    …


Formatting

Please take care to follow Python formatting conventions, especially the consistent indentation by four spaces, especially since whitespace is significant in Python.

year = int(raw_input("Input year: "))

if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0):
    print str(year) + " is a leap year"
else:
    print str(year) + " is NOT a leap year"