Definetly an extra Gig will help, just recently purchased another gig, not a fix all, but definetly a welcome diffrence, still get lag but only in 4000 compression settings, and of course whats happening around your sub.Check your virtual memoery settings, whatever recommend size is, double it,that may help.Sound drivers and video drivers may be problem as well. Research drivers your using and see what others are saying about those particular drivers.Google can be your best friend, also this forum

Have about 200 hours gametime and probly spent 50 hours researching forum and google :tweak XP and others and this is my result
System spec
Win XP
Intel 3.6 Ghz
2Gb OCZ DDR ram
7600 GS BFG Video card 93.71 Driver tweaked driver
Samsung 19" LCD monitor
80 GB HD
AsusPv5PE-VM MB use onboard sound, found that using PCI sound card,driver caused probs IE too many crashes
Do not use free antivirus, firewall programs thay do a reasonable job, but you get what you pay for. Heh! learned the hard way.
you really have to play with your video card settings and SH4 graphic/ sound settings to get the best performance/graphics/ sound depending on your PC specs.
Really luv this game, the potential is there for greater gamelpaly and yeah! I do love the eye candy
Anyhow after doing all this,Post Processing On get a respectable 24FPS on bridge, 36 inside sub, and 72 on world map up to reasonable compression time. Warp speed will cause you lags no matter what you do . Fantastic grahics and very rare CTD with this setup

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