By default, you only have write access to folders and files that are inside your user directory (c:\users\yourname), some hidden folders, and any folder that you have created.
The only time you should need write access to any folders outside of this area is when doing system administration or installing a program.
This can be done easily by running whatever tool or install program you are using "As Administrator" by right-clicking it and clicking Run As Administrator, which will allow the tool to access the system.
This is the new way of doing things in Windows Vista - the system is locked down, and only programs that you Run As Administrator or that automatically ask you for permission are allowed access to your computer. This will prevent programs from gaining access to your computer without your knowledge.
This "Run As Administrator" command is great to run on Windows Explorer, command prompt, and control.exe (control panel).
It is *NOT* recommended that you change the security settings to allow write access to the operating-system created files and folders, as this will greatly reduce the security of your system.
So, in essence, this becomes a permissions/ownership issue. Here's how to deal with both:
To see your permissions, right click the folder/file, click on properties, and check out the security tab. Check to see what permissions you have by clicking on your username (or user group). Here are the types of permissions you can have: http://windows.microsoft.com/en-US/windows-vista/What-are-permissions. You need to be an administrator or the owner to change permissions (and sometimes being an administrator or even an owner isn't enough - there are ways to block even them from access (though a smart administrator knows these ways and can get around them - but usually shouldn't because they were denied access usually for a very good reason). Here's how to change folder permissions in Vista: http://www.online-tech-tips.com/windows-vista/set-file-folder-permissions-vista/. To add take and grant full right permissions and ownership to the right click menu (which will make it faster to get in once it is set up), check out the following article: http://www.mydigitallife.info/2009/05/21/take-and-grant-full-control-permissions-and-ownership-in-windows-7-or-vista-right-click-menu/.
To fix this problem with the folders, take ownership of the folders or the drive (as an administrator) and give yourself full rights. Right click the folder/drive, click on properties, go to the security tab and click on Advanced and then click on the Owner tab. Click edit and then click the name of the person you want to give ownership to (you may need to add it if it isn't there - or it may be yourself). If you want it to apply to sub-folders and files within that folder/drive, then check the box for replace owner on sub-containers and objects and click OK. Back out and now there's a new owner for the folders/drive and files who can change permissions as needed. You can now change them from read-only (even if the main folder says they still are read only - you can have access yourself as the owner). You can keep them as read-only for other users and guests and even administrators (though they can take ownership themselves and gain access if they so desire and there really isn't much you can do to stop this except protect the folder with a password using a 3rd party product). Here's more information on taking ownership of a file or folder: http://www.vistax64.com/tutorials/67717-take-ownership-file.html. To add take ownership to the right click menu (which will make it faster to get in once it is set up), check out the following article: http://www.howtogeek.com/howto/windows-vista/add-take-ownership-to-explorer-right-click-menu-in-vista/.
Good luck and I hope this helps!
Lorien - MCSE/MCSA/Network+/A+