There are a lot of possible reasons you are being disconnected. Here is one
possible fix: Open up the file called DataRate.txt and change the value to 3.0 and save it. Even if this doesn't fix your problem, it won't hurt anything either.
It used to be that low datarate numbers were preferred for dialup and higher numbers for DSL/cable but I have seen posts on the EQ tech boards recently where they are now advocating lower numbers for connection stability regardless of your connection speed.
Sorry to be longwinded but I found this just by chance as well regarding LinkSys routers:
(link) It says:
PROBLEM With Linksys BEFSR81 Firmware 2.42.7.1: regardless of what I'm running, EQ disconnects about every 15 minutes. Its like clockwork. This only seems to effect the EverQuest session (I.E.: the router doesn't reset, just the EQ session). The only clue I was able to find (using WallWatcher) was an inbound connection from EQ's servers that occurred either just before or just after the disconnect. The port it comes in on is apparently somewhat random: above 1024 (I've seen incoming values in these circumstances with a Local Port value in the 1100 to 1200 range: the remote port SEEMS to always be 2737). The solution is posted after that section if it applies to you - good luck.