How can an element of an array be used as a variable name for some of the rest of the data?

What you are looking for is the vars built-in function of python. This will give you a dict representing the variables in scope.

I don't follow the code in your example enough to add this solution into it, but here is an example using vars that might help:

# Set up some data (which would actually be read from a file in your example)
headers = ['item', 'quantity', 'cost']
data = [['dress', 'purse', 'puppy'], [1, 2, 15], [27.00, 15.00, 2.00]]

for i in range(len(headers)):
  name = headers[i]
  value = list()
  for data_item in data[i]:
    value.append(data_item)
  # This sets the name of the header to the name of a variable
  vars()[name] = value

# Print to prove that vars() worked
print 'Items', item
print 'Quantities', quantity
print 'Costs', cost

Which produces the following output:

Items ['dress', 'purse', 'puppy']
Quantities [1, 2, 15]
Costs [27.0, 15.0, 2.0]

Use the int function

with open('x.dat', 'r') as f:
    row = 0
    for line in f:
        words = line.split(',')
        for col in range(len(words)):
            DataMatrix[row][int(col)] = words[int(col)] 
        row += 1
f.close()

Alternatively, you could do a CSV reader to make this marginally easier.

with open('x.dat', 'rb') as csvfile:
    theReader = csv.reader(csvfile, delimiter=',')
    row=0;
    for line in theReader:
        row+=1
        for col in range(len(line)):
             DataMatrix[row][int(col)] = words[int(col)]