I had a similar issue under Win7. I guess it is a file system permission problem. My solution was to create a folder "programs" under my users folder and extract eclipse into that programs folder. I did the same for glassfish so I can be sure glassfish has write permissions to its own folder.
[Message sent by forum member 'jjackb']
http://forums.java.net/jive/thread.jspa?messageID=484011