I really don't see any doubt per say, but here's a few answers....


1. How do you define  content source  in Search?
In MOSS 2007, this is in the SSP

2. Where the index  is stored? (as crawling  creates index to each doc.)
The index is all machines with the sharepoint indexing service installed.
It's easy to find because it creates  a windows network share.

3. Am having 5 Features(f1,f2,f3,f4,f5). Each feature  is dependent  to other
feature.
Now How do i define dependencies  at the time  of deploying  a feature.

There isn't an easy way to do this, the best method is to make one WSP with
all of the dependencies in it.


4. What are XML based  webparts?
XML based webparts? Well I'm not really sure about this one, but SharePoint
lets you export a webpart as an XML file, however, it's not the binaries,
only public properties are exporting such as the title, size and of course
any custom properties you've added.