Hi Vikram,
There is a book called, "Programming the Perl DBI" authored by Alligator Descartes & Tim Bunce. Of all the O'Reilly published books on Perl/CGI, this one has been the most helpful to me in working with SQL, DBI, Oracle and Perl/CGI. It has a detailed comparison in answer to your question in Chapter 7, ODBC and the DBI and gives relevent details as to the differences and strengths.
DBI, as you know, is a Perl module. It is the standard database interface when working with Perl. DBI requires database type dependent drivers - which you may see - such as DBD::Oracle, DBD::ODBC, DBD::MySQL and so on. This really does not complicate matters as much as it sounds. Once you have the DBD setup, it is really cut and paste code afterwards to reuse it.
Win32::ODBC is more closely aligned with Windows products, which may, for some, satisfy their needs. It has extensive ODBC function support whereas the DBI is a little lacking. Also, DBI, is more closely aligned with UNIX, LINUX, and other non-Windows OS's. Win32::ODBC Functions supported include, Tables, Columns, Special Columns, Statistics, Primary keys, Foreign keys, and GetTypeInfo - the DBI supported only Tables and GetTypeInfo as of February 2000.
The advantage of Win32::ODBC over the DBD::ODBC is that most of the ODBC API is available; attributes, options and metadata is available, and most significant - scrolling cursors are supported which is useful in interactive browsing applicatons.
Your best bet for additional information is back to the source - go to Microsoft's MSDN and use their search utility. It used to be
- I'm not certain if it still is but their search answers can be overwhelming so be as specific as you can.
To borrow from the book I mentioned earlier, there are some disadvantages to using Win32::ODBC compared to DBD::ODBC - there are no separate prepare and execute steps, there is no automatic error handling and most significant, Win32::ODBC is slower than DBD::ODBC.
It basically comes down to your needs and at the moment it sounds like you want more of the ODBC API at your disposal which means go with the Win32::ODBC - If you port to non-Windows later, you can use Win32:

BIODBC which provides some emulation of Win32::ODBC. Win32:

BIODBC is bundled with the DBI module. When you're ready to make a change (not including OS/Webserver specific changes) you can change from:
use Win32::ODBC
to
use Win32:

BIODBC
You could even run it from the command line.
perl -MWin32:

BIODBC script_name_here.
If you do make the jump from the Windows ODBC, you really should get the book or borrow it from someone who has it - as I mentioned before - it is the most useful one for me of the O'Reilly Perl books.
Quite frankly, I don't care what webserver you decide to use but your choice of OS has some pretty obvious and well-exploited holes in it. If you're developing for an Intranet application behind a fairly secure firewall/proxy - you might be okay, but you should look to the future and something that has some greater long term reliability. If you are going to have more than a few users relying on this as a platform, it would be worth your time investment to learn and go beyond 98 (your users will thank you too). I'm not an MS basher or an anyone basher for that matter, but while 98 is "pretty" it does not have the reliability of the UNIXalike OS's.
Good luck,
higginsd [sig][/sig]