Ok so I want to call my computer my ferrari. This may be a bit of an overstatement.
But I need to get a new PC.
I play poker online full time. I play 24 or more tables at a time. I use hand history tracking software which displays a "hud" on each table with statistical data on players such as how many hands I have seen this player play, how often they raise, fold, re-raise, etc. This refreshes every 5 secs. I use software that helps by stacking all 24 tables on one location or more and rotates the table next in line that needs action to the front. This software also gives default bet amounts based on % of pots sizes, whic I of course can mouse scroll to change.
I do use dual monitors.
Currently I use a Intel core 2 6400 2.13 ghz vista os
Nvidia 8800gt video card.
I have lag issues when I play tournaments and a table breaks and I get moved.
Your main lag problem is either caused by:
1. slow internet connection
2. more than your CPU can handle
For starters, try overclocking your E6400 to 3.0GHz or above. That chip is very overclockable. Then see if there are any improvements.
Also be sure to monitor temperatures with HW-Monitor and make sure the load temperatures are under 70'C for the cores. Light OC is ok for the stock cooler. If you're using an aftermarket cooler, you should have no problems and can try a 1GHz+ overclock.