Sorry for not replying earlier, I went crazy restoring my DNN database..anyways..yes, I'll gladly provide my setup.

As of now I am running DNN 4.5.0 with a single portal. 
Windows Server 2003
SQL Server 2000
.NET Framework: 2.0.50727.42

I did not change any code in the upgrade other than the proper sections in the web.config (Machine Key, App Key, Conn String)

As I stated earlier, 4.5.1 upgraded fine, but did not authenticate automatically when accessing windowssignin.aspx, same issue with 4.5.2...but logging in manually worked in 4.5.1 but produced an endless loop in 4.5.2 (DOMAIN\UserName).

Also accessing a page in this manner does not auto authenticate in 4.5.0: http://county/Home/tabid/105/logon/windows/Default.aspx
User must go directly to windowssignin.aspx (which isn't a big deal)

I checked the Event Viewer in 4.5.1 when I was able to log in and there actually was an event for Windows Authentication and well as an event for Logging in manually right after that.

I've not read this closely, but might it be the same issue as noted at:

www.dotnetnuke.com/Community/Forums/tabid/795/forumid/-1/threadid/139280/scope/posts/Default.aspx

- John

I am having the same problem on my intranet and I applied the fix referred to in the post referred to above and it did not fix the problem, new users that login do not get an account created in DNN and get the "redirect loop" errors.
Another issue that I noticed was that AD group to DNN roles membership is not working.  For instance users in the Staff group in AD do not get automatically added to the Staff role in DNN even if they already have a DNN account.
Any help would be greatly appreciated.