When Mechwarrior 4 first launched, it had a large multiplayer following. Players could compete against each other across the internet, or even over their home network. The game also received the Black Knight and Mercenaries expansions, adding additional missions and 'Mechs to the mix. These were re-released as free downloads in 2010, along with the Inner Sphere and Clan 'Mech packs.
The latest version of Windows has some issues with the game, especially when using a graphics display driver that it doesn't recognize. You can get around this issue by disabling your graphics card in your computer's device manager. Once you've done this, the game should launch normally (unless it doesn't recognize your graphics card).
If you want to try out the multiplayer features of the game, you'll need a program called Gameranger, which can host matches on a private server. This can be a bit tricky to set up, but once you have it configured properly, it works pretty well.
Unfortunately, MekTek isn't doing a lot of updates for MechWarrior 4. The last time I saw any sort of mention from them was in 2017, when they announced that they were moving away from the BattleTech franchise and making a stand-alone game called Heavy Gear Assault. The servers for that title shut down in August of this year, and there aren't any signs of life on the MekTek Facebook or Twitter accounts.