Hello,
Technically, you can do it, but it will not look nice and may not work at all as reporting services are supposed to be read only.
Create a parameter of a string and add this parameter to your report. I don't know where you want to include your comments, but it can be a textbox or a calculated value for a query (right click the dataset and select Add). The problem is your parameter input textbox is quite small for a good size comment. And another problem - you can add only one comment per a report.
So if you need to add comments for each line in your table, than you can't do it. You need to have a proper interface (ASP.NET or something else) that will give your users ability to modify and add data.
good luck
