Whenever I SHOOT OR ANYONE ELSE SHOOTS (LIKE NPC'S) IF ANYTHING SHOOTS THERE IS LAG!!!

In case this helps: nothing else lags, not even when there's tons of smoke only when someone/something shoots!

I also have my resolution on the lowest and no shadows, and lowest for models!

my computer:

Pentium4 3.00 ghz Processor
512 mb RAM
128 MB Graphics Card!