Rain is part of survival. This server is survival. If rain is lagging you, use a different texture pack or turn off fancy graphics. Nothing much else to be done on this subject.
Crazy is right, rain is part of survival, and the server IS survival, and don't complain about lag, the rest of us have it too you know.
justin the prob is i dont have modloader and i hava a mac.i would if i could. the whole reason i even suggested this is because rain does no more thanobscure vision and make lag. lighning acually can have an effect on things, but rain cannot
As previously stated, this is a survival server, part of that is weather conditions in the wild. Spoutcraft gives you the power to remove rain, make it always day/night etc. Bear in mind though that even if it looks like daylight, it may still be night in the wild and monsters will be out. You have the power to stop the rain yourself. Also if you use spoutcraft you cannot easily use any mods like minimaps/light level displays etc.
you are not allowed to use mods that do not give you an unfair advantage, such as xray mods, flying mods, and the like. also anything recommended by justin AND jermey i am sure is safe to use.
Below is the link to a forum thread which discusses which mods are acceptable and which aren't http://empireminecraft.com/threads/acceptable-mods-links-in-post.512/#post-4007 Spoutcraft does not allow you to use regular mods, they have their own version called 'addons', and they are not as user friendly as modding regular minecraft.
try optifine it has the ability to remove certain things thus causing less lag the change is only client side though so it might appear that it is not raining but it might be on the server