Well, yes the Inspiron 6400 is a nice option but, if smaller the better is the criteria, customizing a 640m (14" widescreen) would be a nice choice along with a dvd writer and a 9 celled battery. This would fit in ur 50k budget.
If you raise you budget by another 10-15k, you can very well have a nice gaming laptop like a
HP dv5100 or be the first customer to get a Dell XPS laptop from Dell India. Just tried to customize the XPS on the lines of the HP's dv5100 both come out for the same price tag. So getting the HP would make more sense.
Anyways, as such, the 640m or the 6400 are nice laptops and truly value for money considering the current market scenario.