My AMD Athlon 64x2 5200+, 2GB RAM, Asus 8600GT Magic can bump up to 40fps with 40 players(39 bot, 1 for myself ) at Max Setting under 1280x960 resolution.
Are you talking about Lag, as in network lag? Or are you referring to Low FPS as "Lag", which it's not...? If it's lag, then sometimes wrong with any routers or network cards you may have or maybe event settings, if Low FPS is what you're talking about, you're lacking the needed hardware or another program is taking up too many resources if you have what it requires.
Finally finding about some of the bots that are flooding the users online - bytespider apparently is a huge offender here - ignores robots.txt and comes in from a ton of different IPs
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.