You're looking at an issue of object persistence, more than likely.
When you close the form, the object that the form represents, including all members included in it, are disposed. More than likely, you'll want to serialize the information in a temp file, or something like that.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dndotnet/html/objserializ.asp
That'd be my guess. I'd really like to know if there's something better.