I have DSL. Every Spearhead server I join, regardless of ping, lags. Some more than others, but they all do it, even dedicated.
So I popped in the original MOHAA and tried it. Same thing. Servers I used to play on every night for months now lag horribly.
This makes me think its not anybody's connection, but something to do with the latest patch for original Allied Assault (which Spearhead automatically installs before installing itself).
Someone told me if you connect directly with their IP and skip the in-game browser, it doesnt happen, implying its a Gamespy problem. I never tried it, tho. If someone else does, please let me know if it helps.