Ping problem

[Tutss]

Hi guys, I'm having a very anoying problem when I play left4dead, I play in a dedicated server. When I keep stopped my ping is great, about 30 ms, but when I start runing the map, when it comes many zombies, horde or horde from bommer vomiting, my ping start growing up and reaching something like 300-400ms. I got a good internet speed (2mb down) and people with a worst internet dont have any lag at all on these hordes.
It looks like something is limiting the package transfer, because only when I got horde (high transfer of package) I have this lag, I would like to know how I can solve it.
Thanks!

[one of them]

Make sure your Steam Settings match your Download Speed.
Go into steam, click File>Settings>Download and make sure the speed is closest to yours.
Also, what is your upload speed? Upload matters more than Download with Online Games, but I doubt it's low enough to effect performance.
Also, what type of internet? Cable, DSL, Wireless, etc.?

[Tutss]

it is 512kbps, i got ADSL with router

[Sofaires]

i have a friend with a similar problem in another game, let me ask this... do your computer handle well the horde? i mean it lags or it is smooth? the reason im asking is cause my friends computer didnt handle that game very good and when heavy fights come the game start laggin and her ping went high enough to kick her out of the game in times like that