You don't say whether the first writing on the CD was also done by the XP CD writing function. This could be significant. Also can you not read any of it?
The XP CD writing format is quite different to others and will not be compatible if the first lot was written using Nero or Roxio. But they don't tell you this in the blurb.
The data is still there on you unreadable disk but it is likely to be unreachable without special facilities. What has probably happened is that the Table of Contents (ToC) has been "corrupted".
I came across the same problem with my new Sony Vaio with CDRW and CDR disks and XP. All those backup disks...
But that's OK, just install your Nero Propriety CD writing package and all will be well.