Optimizing this 'print up to the nth prime number' script
Welcome to programming and code review!

Your code is pretty good especially for a beginner, but I'm going to be picky:

from time import time


I recommend putting at least one blank line between the imports and the code proper

odd = 1


You don't use this until much later. Don't declare variables until you actually need them. It will make the code easier to read.

primes = [2]
n = input("Number of prime numbers to print: ")


Rather than using input, I recommend using int(raw_input(. Input actually interprets the text entered as a python expression which means it can do anything. If you really just wanted a number, using int(raw_input is better. Also, input has been modified in python 3 to be like raw_input.

clock = time()
def isPrime(number):


Typically functions are defined before the actual code not in the middle of it.

    global primes


global is only necessary if you want to modify the primes. Since you don't modify it, you don't need it. 

    for i in primes:
        if i*i &gt; number:


It's not immediately obvious why you can stop here. A comment would be helpful.

            return True
        if number%i is 0:


Put spaces around your operators: %

            return False
while len(primes) &lt; n:
    odd += 2
    if isPrime(odd):
        primes += [odd]


When adding a single element to a list use primes.append(odd)

print primes
clock -= time()


That's kinda confusing. I'd suggest doing start_time = .., end_time = ..., time_spent = end_time - start_time. That ways it clear what you are doing, whereas what you've done with the clock is unusual and not immeadiately obvious.

print "\n", -clock
raw_input()


Also, don't put logic in the top level scope of your program. Put all logic especially loops inside a function. It'll run faster in the function, and will keep the program neater.