Sorry, Anish, you cannot export multi-column layout from InDesign to EPUB. The split/span paragraph style has no equivalent in CSS. It's a great feature request, though: Adobe – Feature Request/Bug Report Form
The work that Walrus Books is doing is pushing the edge of what's possible w/EPUBs. They have an incredible demo of what's possible with HTML 5 and CSS3 in other parts of their site; but I don't know of any visual layout program that can export to that yet. It *might* be possible with Dreamweaver CS 5.1, have you tried that?
BTW that Walrus Books URL you include leads to a post about enhanced ebooks but the post doesn't describe multi-columned layouts. It does show embedded video, and that you can do with InDesign CS5.5.
However at this point only the Apple iBooks app is capable of showing embedded video in an EPUB. They represent about 15% of the eBook marketplace. FYI.
You might want to check out my video on EPUBs at Lynda.com; and/or read Liz Castro's book about it. Those would give you a good grounding on what's possible with real world EPUBs these days and what InDesign is capable of outputting.
AM