The read-only is not easy to explain as you don't give much to go on. If you copy a file from a CD or DVD it will normally have the attribute read-only turned on.
To fix this, go to the Windows Explorer and find the table (the .dbf plus its .mdx and .dbt, if it has either of these). For each file, right-click and choose "properties". At the bottom of the properties dialogue (on the "General" tab) you will see "Attributes". If the "read-only" is checked off, uncheck and click OK.