shoottokill

I don't know if same thing is happening to everyone else, but when I shoot at someone who is moving, he/she loses no HP at all. Sometimes I manage to take my shots with a little leadaim (just like in sa-mp) and it sometimes works (not all the time). One odd thing I discovered is when I shoot where my target was a few miliseconds ago, I manage cause some damage. Anohter weird thing is weapon ranges are insane, people can take headshots with AK-47's from far away. So, could anyone possibly explain me workings of sync shots? Whenever I play gamemodes like Stealth, I just keep getting killed the whole time. One thing I guess I should mention is my computer is 4 years old, could this have anything to do with this? I have Nvidia GeForce 5500 and 256 MB CPU. Yes, I do have a low FPS (25-30), but I played SA-MP with this computer for 2.5 years and its odd for me to be this bad in MTA. There are people from clans like FAS, B2K and PCP who can barely speak english but always put the bullet in the right place, regardless of distance. How?