Ok then, first things first. As far as making backups to DVD I personally wouldn't recommend it although I know some on the forum do. DVD's, like EHD's (external hard drives) can fail, and will at some stage, it's more a question of when. The only indication you will get that your DVD has failed i.e. not readable is probably when you come to need it whereas using an EHD you'll hear it fail and be in a position to do something about it. Additionally, EHD's have a far greater capacity and gigabyte for gigabyte are far more cost effective. You might want to give that some consideration.
As to your immediate problems - I'm not altogether sure what you mean by
or raw that had been opened and worked on. When you work on a RAW file i.e. edit you cannot then re-save the file including your edits as a RAW file - you either have to save out to a new file, either jpeg, tiff or psd. If you don't save out in either of these formats following editing then your edits will be saved in an xmp file that has the same file name bar the suffix xmp and is located in the same folder as the original RAW files. In this case it is important to not only backup your original RAW files but also any edited RAW files plus their associated xmp files otherwise your edits will not be backed up and probably lost forever.
Ok, as to the difficulties in viewing your RAW files from the DVD. Elements includes codecs in the application so that you are able to view your RAW files within that application. When viewing RAW files via the OS (operating system) in Explorer, which is in effect what I believe you are attempting to achieve, then you need additional codecs installed so that Windows (in your case v7) can display thumbnails. These codecs can be found by clicking on this link
http://www.fastpictureviewer.com/codecs/ which I recommended to another user in another thread and who has since posted back to say that everything is now satisfactory. JPG format images will open in any OS as they are not a proprietary format belonging to any one camera manufacturer e.g. CR2 and Canon.
If you do go along with the EHD recommendation at some time in the future then I can personally recommend a piece of freeware called SyncBack. It's an excellent application and does away with the need for other apps such as Nero, Sonic and Co.
By the way, if the solution given in para 3 above works (and it should) don't be surprised if you don't see the edits that you have made to a RAW file being displayed - only the original unedited version. Windows Explorer cannot read xmp files and so just ignores them. On the other hand, RAW files with an associated xmp file will be read by Elements/Photoshop automatically with no action need by yourself. Action will be required however, if you delete these xmp files or move them to a folder other than where Elements/Photoshop placed them originally.
Best of luck.