When you buy an assembled computer you can save up to 10, 000 rupees on rupees 40, 000.The advantages are that you can get a better equipped computer at a price which is lesser and the performance will be better.
The precautions to be taken are. Motherboard should be original have all the required ports such as USB 2.0 etc and enough upgrade options (Extra PCI slots etc). (ie Intel Boxed or VIA Boxed not some cheap one based on motherboards of these companies) You should go in for atleaset 256 MB RAM because it hardly costs more and is really useful. Only install the software you need.Go in for a 17inch monitor rather than an 15 inch it is better for Multimedia applications you can watch movies and better for games.
Use a good Graphics card it helps the operating system work more smoothly (especially if it is Windows XP) Geforce 4 MX440 is a good performing affordable option.
The cabinet should provide atleast 330+ watts of power this helps when you are going to attach scanners printers etc.Make sure the SMPS and the fan are working fine.
Finally the guarantee given by your vendor should be Comprehensive and Onsite not Carry in. Make sure of the terms before you buy the computer. It will help if you take the guarantee terms in writing from him.
Sample Configuration Could be:
High End PC:(Multimedia and Games)
P4 2.2 GHz
Intel 865 Motherboard (Latest with USB 2.0 and on board Audio)
256 MB RAM
GeForce4 MX 440 64MB Graphics Card
17 inch Monitor.
880 Watts Speakers
ATX Cabinet
52X CD Writer(52x Read Speed, 52x Write Speed, 24x Rewrite speed)
16x DVD ROM (Optional)
3.5 inch Floppy Drive (Optional since you have the CD Writer)
56KBPS Internal Modem
80 GB 7200 RPM Hard disk
600 VA UPS from APC
This will be a really good computer and you can use it for almost anything.