In general - regarding this question and others you post (which I just reviewed briefly) - you will save quite a bit of time if you research your problem before posting a question. Not only will this save other people time, this will save time for you as well (so you don't have to clarify your question several times and still receive no answer). Also, you would have greater success if you spent some time learning more about the technologies you plan to employ and developing a solid knowledge of the basics or fundamentals.
If you want a good answer to your question or solution to your problem, you need to give more specifics regarding the problem and your situation, because people can't read your mind and the details you've given aren't sufficient for anyone to even attempt an answer. For instance, what will you need to do with this text-mining system? (when you respond, please don't say, "mine text" - tell us what you mean by that). Are you building the entire system, or merely a single part of it? What parts are currently in place that you must work around - data sources, user interface, etc.? You mention a GUID - what do you mean? I assume you are simply referring to the user interface - is there a user interface and, if so, what kind is it - Desktop, WinForms, WPF, Web, Silverlight, ASP.Net, etc.? Where are the essays going on the user interface? Do you need to choose controls to put the essays into, or do you have controls for them already? If so, what controls are you trying to put the essays into? What is the format of the essays - text files, word documents, pdfs, html, etc.? Where are they coming from - from the internet, files on your desktop or, or from a database of some sort? Do you need to save them to disk, or how do you plan to store them? You don't need to answer all of the questions I've posed above, but you should, at least, address the issues that relate to your question (most of the questions I've posed).
The quick answer to your question is that there is no practical way in which DataSets can hold lengthy strings such as essays (I'm not saying it's impossible, just that it wouldn't do much for you). DataSets hold relational database objects - DataTables - that each have columns and rows.
Consider the design of your project and try to identify a suitable structure. Here's a suggestion: if you don't need to preserve formatting, try putting each essay into a string. Your collection of essays could be held in a generic collection, such as a List (i.e., List). Alternatively, you could look at using a content management system (CMS) to hold the essays. Research those topics and see if you can come up with a usable idea.
Best of luck!