Lecture time! =^_^=
There are two separate factors that come into play when people talk about, "lag." The first is connection latency. The second is graphical lag.
Connection latency is the time it takes packets to get from the game server to you, and back again. For dial-up connections, this can be high - generally around 300 milliseconds (about 1/3 of a second). Since EQ2 isn't a twitch game (FPS, RTS), 1/3 of a second probably won't be much of a problem, assuming you don't get lag spikes.
Graphical lag, on the other hand, is what many people complain about - chunky movement, low Frames-Per-Second, and so on. Your connection speed has no impact on this whatsover. The only thing that does is how high your graphical detail settings are set. It doesn't matter if you're running a top-of-the-line system with all details set to max, or a Budget Box with all details turned down - the server is still passing the exact same data to your client, and vice-versa. If your computer/graphics card gets too much data to display (too many models or models that are too high of detail, especially), your video will freeze or stutter until your system is able to catch up.
A 56k dial-up connection shouldn't be a real problem with any modern MMOs - there just isn't that much data being passed back and forth. Just make sure you've got plenty of memory and a good video card! =^_^=