Just Jane, the most important thing about any video card these days is the Amount of Ram it provides. This helps to reduce your CPU and memory usage.The best cards I believe provide all in one capabilities. Meaning that you can watch TV shows with them without leaving the computer. It's great for not missing a favorite TV show or important news broadcast.
Personally, I will never buy another Nvidia video card. I had a Nvidia RivaTNT 64MB and it went kaput after just two years. That is what forced me to buy a new monitor thinking that was the cause of my video problems. Then, my warranty expired on my computer and I had to buy another videocard on my own. It seems that a lot of those Nvidia Cards, especially the TNT models stop working just after the warranty expires. That sucks!
So, personally, I'll never trust Nvidia again. And, their website won't support the videocards that you get with a system. So, you're stuck mostly with waiting for the computer manufacturer to make updated drivers. Like a computer manufacturer really knows anything but how to mess up you system and hardware.
I prefer ATI video cards. They are becoming more and more popular. I brought a 128MB ATI card and I am very happy with it. Their drivers are awesome and always work. Nvidia drivers were a pain in the neck for me.
Regarding your problem. Most monitors have adjustable h-size and v-size, right on the monitor. If your monitor does it through software, then you will need to find those adjustments. If you are seeming black spaces around your screen, then you need to find and adjust those monitor settings.