IIS 7.5 changed some fundamental account settings. In order to enable write access to both logs and temp, do the following for the folder you wish to modify permissions on (aka, add write):
Open Windows Explorer
Select a file or directory.
Right click the file and select "Properties"
Select the "Security" tab
Click the "Edit" and then "Add" button
Click the "Locations" button and make sure you select your machine.
Enter "IIS AppPool\DefaultAppPool" in the "Enter the object names to select:" text box.
Click the "Check Names" button and click "OK".
Now you can modify the permissions for the default app pool user. This is the new "network service" type user.
Apparently you can add any user to the default app pool in order to keep track of permissions for many different web applications.
This was a big headache for me to find, I hope it helps someone out.