VIDEO CARD
You need one that is not on the mother board it will help your problem.
This is probably the main cause of your video display lag. There can definitely be many other causes, such as amount of RAM and CPU speed, as well as software issues such as malware or continually running applications in the background using up system resources, but usually this is attributed to underpowered graphics. The other thing that could be causing it is not actually underpowered graphics but not the proper graphics driver, just something easy to check!
There are a lot of great options out there for a new computer workstation, but it all depends upon your specific needs. Right now is kind of an iffy point in the market to be making purchases for a new computer, though. Both AMD and Intel are about to release new processors and their matching platforms. Even if you don't go with the absolute latest and greatest, it will undoubtedly cause the prices of existing generations of hardware to drop.
However, I understand that sometimes waiting any longer is not always possible, so if you had to get a new computer right away, I'd suggest using a Sandy Bridge platform from Intel. I've been very impressed with its performance, and have assisted several other sign shops in configuring and assembling such systems and they too seem to be thoroughly impressed with the capabilities of these chips.
As for your specific graphics issue: Graphics cards and the technology behind them has advanced perhaps faster than any other component out there over the last few years. The integrated graphics found on many latest-generation processors and platforms is more powerful than dedicated graphics cards of three or four years ago in some cases! If you are just working with 2D graphics, such as within Flexi, then you really don't need a whole lot of graphical horsepower actually. Most all of the work is being done at the CPU and your graphics is more just to ensure that you are getting high-quality color display, high resolutions, and just as you are experiencing, eliminate large work area lagging. A simple entry-level to mid-level graphics card is more than enough to do what you need and more. For most design systems, a $100 graphics card or around there will be more than capable of doing everything you need.
For some more information I'll point you to another thread that had a lot of information dealing with graphics cards pertaining to the sign industry, and in there I also included some recommendations of hardware configurations at different price points if you're looking to build a design workstation.
http://www.signs101.com/forums/showthread.php?t=77757
Now, the only thing about that is 1) the prices might have changed a bit since that configuration was initially posted three months ago, and 2) it all really depends upon your specific needs.
While the options and configurations given are a good starting point, depending upon the specific needs of your computer system you may have some variations or different hardware that is needed. You can post up on here specifically what you want or need and what you use your system for. I'd also suggest that you give Casey a call sometime at Signburst Computers as he is very knowledgeable and incredibly helpful at making sure you have exactly what you need in a computer system.
