not knowing your video card, it's impossible to say.

if you have a PCI video card with only 1 port, you MIGHT have another VGA port depending on if your motherboard has one.

Most of the current crop of video cards have dual DVI or DVI/VGA ports. Also depends on if your monitors use VGA or DVI. there are DVI<->VGA adapters that you might need as well.

I don't run dual monitors, but consider this: if you add a monitor, you just DOUBLED the number of pixels your video card has to crunch. if you had trouble with one monitor, it's unlikely that you'll do any better with 2.

Good Luck!