I manage a large website with >10,000 pages.  For over a year, the
website has been randomly freezing up, requiring a restart of IIS. 
The website was recently moved from a Windows 2000/IIS 5/SQL Server to
a Windows 2003/IIS 6/MSDE configuration, and the freezes intensified
from every few weeks to every few hours.  With IIS 5, I could just
restart IIS, but now I must restart the IIS service.  The IIS
administrator shows absolutely nothing wrong, and there is no pattern
I see to the hangs, other than high website loads.  I believe that the
ASP pages seem to crash before HTML or Perl pages in IIS when the
hangs occur.

I have had several hypotheses about the problem:  It runs Perl for the
blog, which uses 100% of the CPU power when posts I made.  I have
since moved it to Apache to host the blog.  I removed all the
Application.Lock commands from ASP.  I have tried to close all unused
ODBC connections.  I have tried DSN and DSN-less connections.  I have
removed all the Application-level variables I can and trimmed
global.asa to the essentials.  I have tried to optimized the
efficiency of the SQL code (had to, since we moved to MSDE.)   I have
gone through Google and MS technote articles without luck.

More background:  The ASP code for the website is eight years old,
with parts being gradually converted to .Net.  I am considering moving
much of the website to MySQL (would this help?)  The database
connections currently use a single DSN session variable for the entire
site.  The MSDE db goes over the 8 query limit hourly, which I believe
is non-significant.  I set the IIS recycle settings tighter than the
default to try to kill any hanging connections.  I tried running the
IIState tool before and during hangs, without any obvious patterns,
but will send it if you?re interested.

I did see a quite of few of these in running and hung IIState dumps:

Thread ID: 12
System Thread ID: 914
Kernel Time: 0:0:0.0
User Time: 0:0:0.0
Thread Type: Possible ASP page.  Possible DCOM activity
Executing Page: Unable to locate ASP page

We are quite desperate to get this issue resolved, and will give you
any information or pay whatever it takes to do so.

There could be a lot of problems here.  Just some basic questions for
you to start... are you running the web app in high isolation/low
isolation (in w2k3 I guess the equivalent question is whether app is
in its own pool or not)?

What is your connection methodology?  Are you opening early and
releasing late?  I assume when you refer to the dsn being cached you
mean just the dsn name and not an actual connection?

What is the overall architecture (any COM objects?  Are you using any
poorly-scaling objects such as some office COM objects, etc.)?  Have
you done stress testing to try to find the source of the problem?

Since some of the site is running as ASP.Net the isolation level means
nothing.  ASP.Net does not use isolation levels.