Tom, there's no real difference between the two media. The CD/DVD manufacturers couldn't come to a decision about which standard should be used so we ended up with both technologies.
The way to get either the DVD+RW or the DVD-RW to work is to check that you have a CD/DVD Re-writer drive fitted in your PC. If it is rejecting one or the other, then your drive is not compatible.
On my main desktop PC, my LiteON CD drive is only capable of using re-writeable CD's but not DVD's. My laptop is capable of writing to DVD's and CD's, so I've got an alternative machine to use without having to replace my desktop drive.
Do a Google search on the make of your current drive and see what specifications it gives, to see if it is DVD re-writer enabled.
If not, then you will have to buy an appropriate drive my friend, and either fit it yourself or get someone else to help you.
Laurie.