0 Suggest a laptop within Rs 25,000

For laptops in that price range, you're going to have to make a sacrifice, whether with the processor, the RAM, the hard drive or the screen size. So, first figure out which of these matter more to you.

Keep in mind, the processor and screen size are things that you'll never be able to change; RAMand hard drive can always be upgraded later.
The Toshiba Satellite C665-P 5211 ( 24,500 approx) features a 15.6-inch screen, 4GB RAM and a 320GB HDD. The only downside is that it's powered by an older Intel Pentium Dual-Core processor. Still, this will be enough for office usage and web browsing, but high-end multimedia and gaming will suffer from poor performances.
AMD's APU Dual-Core processors have also proven to be credible performers, and the SamsungNP305U1A ( 23,900 approx) and the HP Compaq CQ43-405 AU (22,500 approx) seem like good prospects.

Samsung has the 500GB of hard drive space you're looking for, while HP will give you a larger 14-inch screen. The built-in Radeon graphics won't give you crystal-clear visuals, but it should handle multimedia and basic gaming well enough.