Parsing out excel's .xls textboxes?

Hi, I have an excel parser I found out on the net a while ago. It does a really great job untill now. I need to parse out an excel file (.xls) with excel's textboxes in it, I want to fetch the textboxes content from the .xls somehow. I have no idea where to look out for this, I have even considered trying to understand the structure of a common .xls file by myself but I even don't know what direction I should be heading to! If you have any idea, suggestion, anything that might help, feel free to come up and surprise me ;) Thanks in Advance, Nitsan