You could do

import random

print """\t\t\tWelcome to \"Guess the Number\"!
\nThink of a number between 1 and 100.
try to guess it in as few attempts as possible.\n"""

number = input ("Enter the number: ")

guess = random.randrange (100) + 1
tries = 1
useds = []

while (guess != number):
        if (guess > number):
                print "You chose", guess, "the number is Lower ..."
                useds.append(guess)
        else:
                print "You chose", guess, "the number is Higher ..."
                useds.append(guess)

        guess = random.randrange (100) + 1
        if guess in useds:
                while guess in useds:
                        guess = random.randrange(100) + 1
        else:
            tries += 1

print "You guessed it! The number was", number
print "And it only took you", tries, "tries!\n"

raw_input ("Press <ENTER> to exit.")