Expanding Search to Subfolders

[PipedreamerGrey]

This is the beginning of a script that I wrote to open all the text
files in a single directory, then process the data in the text files
line by line into a single index file.

os.chdir("C:\\Python23\\programs\\filetree")
mydir = glob.glob("*.txt")

index = open("index.rtf", 'w')

for File in mydir:
    count = 1
    file = open(File)
    fileContent = file.readlines()
    for line in fileContent:
        if not line.startswith("\n"):
            if count == 1:

I'm now trying to the program to process all the text files in
subdirectories, so that I don't have to run the script more than once.
I know that the following script will SHOW me the contents of the
subdirectories, but I can't integrate the two:

def print_tree(tree_root_dir):
    def printall(junk, dirpath, namelist):
        for name in namelist:
            print os.path.join(dirpath, name)
    os.path.walk(tree_root_dir, printall, None)

print_tree("C:\\Python23\\programs\\filetree")

I've taught myself out of online tutorials, so I think that this is a
matter of a command that I haven't learned rather a matter of logic.
Could someone tell me where to learn more about directory processes or
show me an improved version of my first script snippet?

Thanks