I duno bout u, but i use Zone Alarm Firewall. The first thing i did was that i added the parameter "at&d0" to the modem conn settings. It REALLY helps. Im telling u. Next, put a pass lock in Zone Alarm 4 "a3client.exe, launcher mfc ???, generic host 4 win32 processes". After that, engage the internet lock and start A3. I noticed a considerable decrease in lag. I.e. to say that the updater loaded in less than 30 secs (earlier it was like 3 mins+). But still the game lagged. So i did sumthn else to "stay connected". Well go to command prompt or type "command" in run, and ping ne hell of address u no.
eg. ping yahoo.com -t
The "-t" is important as it makes the pinging going. Or simply make a .bat file and include "ping xyz.com -t" in it and run it every time u run A3.
Oh yea, u also have to pass lock 4 "TCP/IP ping command" in Zone Alarm.
Well that Really helped me coz now i cud do the quest of slaying 10 memoras in 1 go

So, thats just my 2 cents. If ne1 else also finds it useful, temme bout it. If ne1 dosnt, temme bout it.
Also, do it on ur own risk, Im not responsible 4 nething goin wrong bcoz o wat ive said ( it shudnt coz nothn is going wrong, but just in case

Thx
Bye
P.S. I run my internet on 56k dialup VSNL.