Network failure when using urllib2

[jdvolz at gmail.com]

I have a script that uses urllib2 to repeatedly lookup web pages (in a
spider sort of way).  It appears to function normally, but if it runs
too long I start to get 404 responses.  If I try to use the internet
through any other programs (Outlook, FireFox, etc.) it will also fail.
If I stop the script, the internet returns.

Has anyone observed this behavior before?  I am relatively new to
Python and would appreciate any suggestions. 

Shuad