I had the same problem and worked on it for a few hours today (not a
computer expert) and found a solution. If you have windows Vista and
want to Right Click, Send to Mail Recipient and have open with Outlook
2007 but can only get windows mail to open or while adjusting settings
and testing, keeps defaulting back to windows mail, or no response at
all , try the following things. (in no particular order)

1. Start: Default programs: Set program access and computer defaults:
Custom: under choose default email program click the radio button that
says use current email program then also make sure the windows mail
radio button is empty and the box next to it enable access to this
program is unchecked ((you will no longer see windows mail in your start
menu and some other places) (note: this final step may not be necessary
if you still want access to this program maybe ok to keep it checked))

2. Start: Default programs: Set default programs: (if completed the
above step you might not see windows mail listed anymore). Click
Microsoft office outlook. Click set this program as default, after you
should see the message directly above "this program has all its
defaults.

3. Start: Default programs: associate a file type or default with a
program. click current default to alphabetize the default programs list:
scroll down look for windows mail, if the .eml file type is still set to
windows mail change it to outlook 2007 by clicking change program:
browse search and select outlook.exe

4. After did all of the above was still not working for me after many
attempts, so I then went online with internet explorer, from any website
click on any send to: email address to send mail, now an outlook 2007
message window should open. Close it. Now in windows try right click
your file or image: send to : mail recipient. It should now be working
properly and finally open an outlook 2007 message window with your
selected file/s attached.

I don’t know why this final step #4 fixed the problem when all else
failed. I assume that somehow opening outlook 2007 from internet
explorer in this way created a missing file or setting that enabled
windows vista Right click : send to: mail recipient function to work
properly. I don’t know if this had anything to do with it but I changed
my windows User name a few weeks ago when the system was new after
installing outlook 2007 and afterwards I was still seeing remnants of my
old user name in some systems files or settings so I changed it back to
the original user name also (before step #1-4) so changing my user name
likely did not have anything to do with the fix/solution above and not
needed to fix but might have been the reason for the failure. I’m
curious if anyone else that is experiencing this problem also changed
there user name before experiencing this trouble. I never used the right
click send to mail recipient function before changing my user name so
not sure if this was the cause.

Edit to my last posted solution for those experiencing this problem.
After changing your settings in #1-3 mentioned previously.

revised step #4: opening a send to: email window from internet explorer
online with outlook 2007 and keeping it open will allow you to
successfully “right click send to mail recipient” in outlook 2007 as
long as the email window you opened with internet explorer remains open
but shortly after closing that same email window outlook 2007 (which was
running in the background(if was not previously open) will shut down and
the right click send to email recipient function will stop working. If
you already had outlook open or open it while the internet explore
opened email is open the right click function will continue to work with
outlook until you close outlook even if you close the internet explorer
opened email. If you close the emails and outlook and you later reopen
outlook the “right click send to mail recipient” function will not work
unless you open email window from within internet explorer again fix
mentioned above. For example go to any websites contact us page and
click the email or link to send email, once the outlook email window
opens if you already have outlook open or open it then you can close
that email without sending it and now your windows vista right click:
send to: mail recipient: will work with outlook 2007 until you close it.
This is obviously not a permanent solution. If anyone has the permanent
solution (aside from reinstall outlook 2007 or windows) please post it.