The S. Korean defense minister has promised retribution for 'those forces which made our officers and men sacrifice their lives for their country'. N. Korean involvement hasn't yet been proved but there is a team of highly trained naval experts examining some suspicious aluminum fragments; a integral part of torpedoes.
This article puts it more in a business perspective than the other one. And it is true that the government is downplaying the involvement of the North, but it doesn't prevent rampant speculation from the media and the people of South Korea. At the end, it does mention that Kim Jong-Il is supposed to be meeting with China, and there has been confirmed news reports of an armored train arriving in China from North Korea. It is believed to contain the Dear Leader himself.
Personally, I think this is all just trying to psych the enemy out for the World Cup. They take their sports very seriously here and its the first time that North and South Korea are both going to be participating.