Project Euler Problem #4 - Palindromic number (Revision 1)
You were on the right track starting with number.ToString().  However, you don't need to duplicate the string, just check whether the value at each index is the same as the value at the index the same distance from the other end:

bool IsPalindrome(int number)
{
    string num = number.ToString();
    for (int i = 0, j = num.Length - 1; i &lt; num.Length / 2; i++, j--)
    {
        if (num[i] != num[j])
        {
            return false;
        }
    }
    return true;
}