Windows 98 is able to use 2 monitors at the same time.
Here are the steps to have the feature working.
The primary requirement for multiple display support is
that the display adapters must be Peripheral Component Interconnect (PCI)
devices, or Accelerated Graphics Port (AGP) devices.
To enable multiple display support, follow these steps:
1) While the computer is turned off, add any additional display adapters and monitors.
2) Start Windows. Install the display adapter and monitor drivers if necessary, and then restart your computer if you are prompted.
3) Click Start, point to Settings, and then click Control Panel.
4) Double-click Display, and then click the Settings tab.
5) In the Display box, click the adapter you want to use, and then click the "Extend my Windows desktop onto this monitor" check box to select it.
6) Click OK.