|Although I do not have dual monitors set up on my 7 machine, I do recall this being an issue for me as well, until I discovered in the display settings you can actually grab and drag the monitors around. By what you are describing (If I understand correctly) windows thinks the left monitor is on the right, and the right monitor is on the left.|
Right click on desktop, personalize, display, change display settings. This is where it APPEARS to be. Without having dual monitor setup I cannot tell for sure. You would just left click and drag one monitor across to the other side of the other. Then windows knows what order the monitors are on your desktop. If the settings aren't in that specific location, try looking around in that area. You would not believe how many times I moved monitors around, or plugged them into different ports before I learned this.
P.s. Another nice feature of this, is that it allows you to set the monitors up anywhere. One ABOVE the other, or even not exactly parallel. Its a neat feature if your monitors are not exactly side by side.