I have set WarCraft 3's video setting to the lowest, without going totally ugly, but everytime I play a game, it's kinda laggy, especially when against 4 computers, with 3 computer allies.

Will lowering down my video card's hardware acceleration improve performance? I have 256 MB of SDRAM, but it doesn't seem to be enough for my settings.

What settings would you recommend to get a lag-free (or at least minimum-lag) from WarCraft 3? I am most probably buying more RAM soon. I know DDR improves performance, but I already have an SDRAM, and I can't mix and match DDR with SD.

disabling hardware acceleration such as smoothvision, antialiasing or aniostropic filtering will improve performance without making your game look terrible. Also, try to see if you can overclock your card.
If youre getting new RAM, and you cant get DDR, I suggest getting Corsair PC133 memory with a CAS latenc of 2.5 or lower. (make sure to check if your motherboard supports ECC)

Try getting a better video card and download drivers.

I had found the anisotropic, etc options once in my comp, but can't seem to find it again. I have a Nvdia GeForce 2 MX 400.