First, make sure that your video card is supported and listed in either the Tier 1 or Tier 2. Each version of RedHat supports different video cards, as newer video cards are released every month and drivers for these video cards need to be written and integrated with the newer versions of Linux.
If the computer that Linux will be installed on already has an OS on it, it should be fairly easy to located the type of video card installed on the system. In Windows 95 or 98, go to the Control Panels, System. Within the System list is an item called "Display Adapter." Copy the information available there into a notebook for later use. Other Operating Systems will require some more work to determine the type of display adapter, and many display adapters are built into inaccessible locations in more modern computers, so locating the card to physically check it may be difficult.
The information regarding the monitor itself should me more accessible. The monitor itself is likely to have its type and make stamped on it, someplace. Research into the company web pages will generally result in the horizontal and vertical refresh rates of the monitor, which are necessary later on if Linux does not support the exact monitor type. Monitor output is produced by scanning a narrow beam of electrons line by line across the back of the monitor screen. The electrons turn on or off the display points of the screen. The horizontal refresh rate of the computer is how fast the computer can scan across one line of the monitor's screen. The vertical refresh rate is how fast the computer can scan every line of the screen.
If RedHat does not support your monitor, it can be manually configured during the install process. Write the refresh rate information down in a notebook, as it is needed to manually configure the unsupported video card.