Script to copy variable into xml file

All,

I think this will make the most sense if I give a little background on my scenario.

I have some software that parses an .xml file for login information (username and password). In the past, we've been using the same username and password for hundreds of users for this software and it has become a security concern. I can easily replace this .xml file with new login information but I need a little help getting the usernames into place for hundreds of users.

So far I have generated an XML file for each computer that needs to be copied to.

For example:

Computer1.xml
Computer2.xml
Computer3.xml
...
Computer290.xml

The XML file itself goes something like this:

<username>JOHNDOE</username> 
<password>PASSWORD</password>

I get that storing a password in plain text is a terrible idea, but unfortunately the software is old and doesn't support another method.

I have a csv file that contains usernames and which computer they use.

e.g.

User1 --> Computer1
User2 --> Computer2
User3 --> Computer3

How can I take those usernames and pop those into the xml files so that they correspond to the correct computer name?

I appreciate any help you can give on this!