It's probably best to install a video card especially if your computer is somewhat old.
You'll need to find out if you have an AGP port or a PCI-e port for the graphic card. An inexpensive one should do the trick. Something like a HD 4350 will be fine.
If you don't have either an AGP or PCI-e port, then you'll need to buy a HD 4350 for a PCI port. That will cost a little more because the PCI port is very old and have limited production.