Words dictionary out of a text file
Some in-place improvements you could make:


PEP-8 recommends four space indentation, not two;
collections.defaultdict would allow you to scan the list of words only once, without having to explicitly initialise to 0 for each word. Even easier, there's a collections.Counter, too;
Rather than iterate over all of the characters you want to replace, you could use re.sub with a regular expression pattern matching those characters (or re.findall for the characters you do want); and
You should generally use the with "context manager" to handle files; see e.g. the tutorial.


More broadly, though, you have one function with three different purposes:


Handling the file;
Cleaning up the text; and
Counting the words.


Splitting these separate concerns up into separate functions would make those functions easier to test, understand and reuse.

With these ideas applied, you could write something like:

from collections import Counter
import re

def get_text(filename):
    """Read and return the content of a specified file."""
    with open(filename, "rU") as handle:
         return handle.read()

def clean_text(text):
    """Lowercase text and extract words."""
    return re.findall("[a-z]+", text.lower())

def get_word_frequencies(filename):
    text = get_text(filename)
    words = clean_text(text)
    return Counter(words)