A friend of mine had this same issue and I remembered that we found a forum hit on google for the problem: http://forums.java.net/jive/thread.jspa?messageID=400088
In my friend's case, it was a folder permission issue.
I think you could check for permissions in Windows 7 the same way you do in Windows XP (I use XP still), so I am guessing here but try:
Right click on the folder, and choose "properties" > select the "security" tab > select the user you are starting Glassfish with and check the permissions.
As for checking if Glassfish is already running, you should see a java process running and sucking up a bit of memory (try using task manager)
I am not sure what information is shown in Win 7 task manager, you could use Microsoft's sysinternals "process explorer" to give you more information regarding which java process is which.