I would strongly recommend keeping at it with mouse and keyboard if you intend to play multiplayer at all. All else being equal, a really good joypad gamer would probably be at a disadvantage against even a mediocre M+K gamer. This is because the joypad controls on the console versions include a degree of auto-aim that's not present on PC, so it's much harder.
Try playing through the main single player on easy with M+K and you'll find yourself getting the hang of it.
If you just want to play SP then as DG says, something like xpadder might work.