You can only turn off the Adobe Reader 7.0 plugin if you use an adminstration account and then you have to copy the preference file to the user accounts.

Notes from another posting of mine:
If you can't get the Internet preferences disabled in Reader 7.0 in the non-admin accounts either copy an admin preference file "com.adobe.Reader7.0.plist" or try editting that file using the Property List Editor (if you installed the Developer Tools).

Under the section Originals, look for BrowserCheck and BrowserIntegration. If BrowserCheck doesn't exist select Originals and clcik button New Child, change the "New Item" to "BrowserCheck", change it to an array, then expand the disclosure triangle and press New Child, change it to "Number" with value of 0 and hit "New Sibling" button and change it to Boolean with value of No.

If you convert it to text you would get:

<key>Originals</key>
<dict>
<key>BrowserCheck</key>
<array>
<integer>0</integer>
<false/>
</array>

Next do the same for BrowserIntegration if it does not exist.