If you're up for trying a free / open-source offering, I've used the Cygwin distribution of fetchmail with success before. I had it running as a "Scheduled Task" every 5 minutes for the better part of 2 years with no problems. It speaks plain ol' SMTP, so although I was using it with Exchange 2003 it should work fine w/ Exchange 2007.
Rather than doing a full install of Cygwin onto my server computer, I opted to pull apart a working install and figure out what .DLL files were needed to make fetchmail work. I also wrote a little script to call fetchmail as a Scheduled Task (because fetchmail needs the HOMEDRIVE and HOMEPATH environment variables set).
If you want my fetchmail "distribution" you can grab it at: http://opensource.wellbury.com/projects/minimal_cygwin_fetchmail/
Dump all the files into "C:\Program Files\Fetchmail" from the ZIP above.
Create a user for the Scheduled Task to run as. The fetchmail user can (and should) be an unprivileged user, but you'll need to grant the built-in group "BATCH" "Read / Execute" permission on "%SystemRoot%\System32\CMD.EXE" in Windows 2003 and newer OS's (I bashed my head into this issue for hours... see http://support.microsoft.com/kb/867466/en-us for details).
Temporarily grant the fetchmail user "Logon Locally" rights and logon locally. (This is an easy way to get the fetchmail.conf file owned by the fetchmail user, and allows you to test the configuration before you make it a Scheduled Task.)
As that user, create a ".fetchmail" folder in its user profile directory. Create a "fetchmail.conf" file in the ".fetchmail" folder (I put a sample fetchmail.conf in my ZIP file).
Using the "do-fetch.cmd" script, verify that fetchmail works properly from the command-line as that user. The STDOUT and STDERR output of each fetchmail run get logged into the .fetchmail folder.
Remove the "Logon Locally" right for the fetchmail user and setup a Scheduled Task to call the "do-fetch.cmd" script as that user (which will, in turn, grant that user "Logon as a batch job" rights).
This isn't the most current verison of Cygwin or fetchmail, and there may well be security vulnerabilities. This all worked for me, but you might want to download the most current versions of all the files in the ZIP, replace them, and verify it works properly.
Like Sam says, you really should use SMTP to receive your mail if you can, but sometimes you have to do what you have to...