I have created a content type and added an image field with unlimited option. Now I want to setup a views slideshow. Some nodes have single whereas others have multiple images. So my slideshow should show single image as well as all the images if the node has multiple images grouped together.
jags, if you are using the Media module, this might be what your looking for: http://drupalmedia.freeworldmedia.nl/book/howtos-guides/how-use-views-slideshow-and-media-2x-module-create-slideshow
True, it's actually for the 2.x version that's still in development, but it offers a lot of information that's also still kinda valid for Media 1.x.
You can group images together in Views, edit the Image field in Views, you'll see an option for 'multiple values'. That's where you can define this.