I use Windows Media Player. I create a playlist but can not burn it to
a previously written on CD-RW. ( it will burn to a fresh CD-RW)It will
not overight even if there is very little data on the disc. I am used
to using tape cassettes. What
is my Problem?

Are you burning a music playlist? If so, I would reccomend using
itunes, which you can get for free at www.apple.com/itunes/download
Once you have itunes set up, just drag the music files into the
library, create the playlist and click burn(it is located in the top
right corner). Hope this solves your problem

You need to erase the CD-RW before you can write onto it. If you want
to have a disc that you can keep on adding more information onto it,
they you must not finalize the disc before your done. If you finalize
a disc you cannot add more information on it unless you erase the
whole disc. Programs like Windows Media Player automatically finalize
a disc after recording. If you use a more customizeable program, you
can set it up so that it won't finalize the disc after recording. The
only cons about not finalizing a disc is that you run the risk that
you'll be unable to read it on a different system/CD-Player (if you
have an audio CD). Free programs that can do this are: CDBurnerXP,
DeepBurner. Search them up on Google to download them.

What operating system are you using? If you are using Windows XP, if
you insert the CD-RW, and right click it, there should be an option
that says "Erase CD-RW".

Eventhough it is call reWritable the files on the disc cannot be
updated, The disk will need to be erased and then write on once more.
dont forget to copy files from cd to computer before erasing.