Upload Excel Spreadsheets into DataGrid

I have several pages in an ASP.NET application where I have datagrids that users can enter information into. These datagrids have a few pre-defined columns. Some users may have this data in Excel spreadsheets on their systems. These spreadsheets may not correspond exactly with the datagrid format. They may have extra columns, differently ordered columns, etc. I would like to have some way to allow these users to upload their spreadsheet, and have it populate the datagrid.

Does anyone here have any experience with this? How did you accomplish this? Third party tools?

I am not looking for links to product web sites. I can google that. I want someone who has actually used the tool and can tell me how their implementation worked out.

Thanks