i love combat arms..
ive even hacked it before, and im not talking with one of those stupid public hacks, but a program that i made..
then nexon had a bigass update, i couldnt hack it anymore, and gave up lol.
but on subject..
google a program named Game Booster, download it, instal it, and run it.
Itll close all of the unnecessary programs you have running on your computer, so that your cpu wont be so busy while youre playing ca.
Also, Defrag your hard drive every week or so, to clear up space on your computer.[start menu>accessories>sys.tools>disk defragment]
If you still experience lagspikes, then im 100% sure that its your internet. Well, possibly a virus, but i highly doubt it.
Ill go ahead and guess its your internet, since its pretty likely. Theres not much you can do about it, you could try using a different router, but that might not even help at all.
And btw, lagspikes are normal for most people on ca, since its such a populated game and the servers can only do so much.