There is an apple document that details a troubleshooting list:
http://docs.info.apple.com/article.html?artnum=306640
In particular:
o Is your iPod charged (it won't be recognized unless it is charged)
o Does it show up correctly under system devices (under USB devices!) and is it using the correct drivers (the one's you just installed) - if not, then you still have a driver issue (also, if you had an older version of iTunes installed and then upgraded to a newer version, you may still be using the old drivers from the first install)
o Is the 'Apple Mobile Device' service running? If that is not running, iTunes will not know that the iPod is there.
If you go through that list you should get a pretty good idea what is going wrong. That is not to say that there are issues with the iPod/iTunes that are beyond drive/device recognition.
All that assuming that you are not using the Windows Media Center edition, since that apparently does not support the iPod.