Can anyone tell me what changes I need to make to my game setup in order to stop lagging or slowdowns in MP? When I enter some servers, they say that my system slows their game down and causes "hesitations" or "hiccups" to occur in performance. I also get this problem on my end. It really takes away from having any fun when I play. Many thanks in advance.
Lag kinda depends on your internet connection and how far the server is from you(and also the servers internet connectiong). Generally, stick to servers within the area you live in. For example, if you like on the East Coast of North America, then stick to servers in that region... don't even attempt to play on like an Australian server :p I stick to servers where my ping is below 150.. anymore than that and I know gameplay will be choppy. It also depends on the servers internet connection, even if the server is right next to you, if they're on something really slow (slower than cable.. though even cable connections aren't too good with servers) then you obviously expect lag. Same goes for you, if you've got a slow internet connection you really shouldn't expect lag-free games ;)
Anyway, look around, try and find servers you like near you (or as close as possible). If there are many players in a server, everyone gets lag too because the server has a lot of load and thus gives some minor lag.
I would suggest using a server-query program like Pathfinder. It pings servers from YOUR computer (compared to GSA which pings servers to their master server so it isn't accurate.. same goes for JK2's in-game server browser.. it's pinged to the JK2 master server). There is an option in GSA (GameSpyArcade) to only list servers in your own country.. which is kinda helpful too.