Sometimes, outlook express blocks attachments and hence does not allow you to view them.
It may give out a message something like this:

To resolve this issue, you need to turn off the "Do not allow attachments to be saved or opened that could potentially be a virus" option:

1.) Start Outlook Express 6.
2.) On the Tools menu, click Options.
3.) Click the Security tab, click to clear the Do not allow attachments to be saved or opened that could potentially be a virus check box under Virus Protection, and then click OK.

Now close Outlook Express 6 and the settings will take place once you restart the email client.