@Luv / Not sure if I understood fully your reference to excel.exe vs the resize with a mouse drag scenario described in your question, but I will try to respond with what I have been able to work with so far in regards to DataTables plus some reading and considerations while browsing their website (http://www.datatables.net)
There is a very cool plugin (haven't tried it myself) that allows you to do CRUD (Create-Read-Update-Delete cycle of programming.. In case that you are working with some local storage or a DB based approach for holding your applications Data) Furthermore, I can't really guess which is the functionality that you are finally aiming to, here are some thoughts to consider:
Paid Plugin for DataTables (Editor plugin)
http://editor.datatables.net/release/DataTables/extras/Editor/examples/events_keySubmit.html
Costs like $15 bucks for the license, if I am not mistaken, but comes built-in with a bunch of ready for CRUD developing api, which seems really cool.. I think that it uses some sort of facebox modal window opening on triggered events. Worth a try!
If you are wanting to edit the DataTables inline, I think that there is a plugin for that
http://datatables.net/release-datatables/examples/api/editable.html
(dataTables created by Allan Jardine appears to be very supported by it's community and I would suggest that if you are planning on developing with it, you ought to become a regular at their forums, or posts questions to Allan as far as if that desired functionality you are looking for has been developed for this current stable version of his interesting work).
On the other hand, if what you are looking for is to edit the columns width as a jQuery UI resizable method, I believe that you need to hook the function redraw, and write a custom extension of something like this example:
http://datatables.net/release-datatables/examples/api/tabs_and_scrolling.html
Also, you might be interested in looking at: (http://jqueryui.com/resizable/) to learn more about how you can prototype reworking the columns on fnReDraw (which is very useful for hooking events when we use the sort by or filtering options from DaTatables) with some chained events programming.
I have not tried this, but it could work as a last resort... Happy coding ;)