When changing permissions from Vista, you need to take care you do not
change ownership or modify the permissions already on the files... you are
just needing to add a permission.
Unfortunately, Vista makes this exceedingly difficult.

To do it properly in Vista:
1) Open an "administrator/root" explorer
- Click start
- Type explorer
- right-click windows explorer
- click run-as administrator
2) From the admin explorer, allow access to a folder
- Browse to the folder you need access to
- Right-click it
- Click Properties
- Click security tab
- Click Edit
- Click Add
* If only your account needs access, type your username
* If every account on vista needs access, type: Users
- Press enter
- Click the checkbox under Allow next to Full control
- Click OK
- Click OK
NOTE: You may also have to repeat step 2 for folders within the folder you
just set the permissions on, if they were created by the operating system.
Repeat step 2 for all folders you need access to.

(thats how it was done on the beta's it may still be the same on the release, but im not certain)