Okay, in answer to your first question. The difference between the 8,9 and 200 series is performance and cost. 8 and 9 series can be bought for a reasonable price where as the 200 series will cost alot more. In answer ot question 2, well htte GT220 will leave the other graphics cards way behind. The performance is far superior and obviously haviing DDR3 triple channel memory gives this card real muscle for gaming. If you can affoord it buy it. Lastly, yes the card will be rcognised by your motherboard. However you must check that your power supply unit has enough power for the graphics card to run properly. I know some of the GT series cards need at least a 750 watt power supply.
Have you thought about Nvidia 9800GT. OK, so it is somewhat old but since you are in India (like me), you can try it out. I bought it last month (1gb ddr3) for Rs. 5,800. It is a reasonable card, and for me with not much interest in gaming, a very reasonable choice. My previous card was 7200 which had some problems with win 7 (deskop icons not loading, etc). For what it is worth, 9800GT gives a win 7 performance index of greater than 6 (perhaps 6.5). My win 7 performance index has jumped from 3.2 (based on the lowest figure which was for 7200) to 5.9 (based on the lowest figure which is for hard disk).