Ok...first off...you need to pacth up the game if you only have the stock game installled...
Then...you need to register a basic account over at Game Spy.....they do have free accounts...
You CAN do this in the multi player screen...
Then..when you start the game...you go to the multi player menu...
Click "join Dynaverse"...
Log in...using your gamespy account information...
a list of servers should then pop up (if there are any servers being run at the moment)....
A note: most of the SFC community is now playing SFC2:Orion Pirates wich can be found on E-bay for a few bucks