I have an old drive cannibalized from a now non-existent computer. It is not now a boot drive. It has a 100MB OEM partition on it and I can't do anything with it. How can I recover that lost space without reformatting the whole drive (which has lots of valuable data on it)? I am running Windows 7, and doing whatever needs to be done with native Windows 7 tools would be a benefit, although not essential.
You should be able to do this with Disk Management. Delete the partition you don't want, and extend the main partition. You can also use Partition Magic or some other such software to do it for you.