Before jumping the gun here people should perhaps conduct a little research - here is a fairly comprehensive and neutral synopsis
http://hoangsa.org/tailieu/The...
The Vietnamese government has explicitly acknowledged Chinese sovereignty over the South China Sea islands and territory in writing
F - Wikipedia, the free encyclopedia... . Furthermore the Vice Foreign Minister of the DRV (North Vietnam) Ung Van Khiem admitted Chinese sovereignty over the Spratlys and Paracels and another Vietnamese official, Le Loc (Temporary Head of the Asian Mission), confirmed that position. On 15/6/1956 Ung Van Khiem was hosting a visit from the Chinese temporary ambassador in Vietnam and is recorded as saying that: “According to documents that Vietnam has presently, historically speaking, Tay Sa and Nam Sa islands belong to China.”
http://tinyurl.com/vn1956abrog...
The Republic of China (Taiwan) which ruled mainland China before 1949 also claims all of the Spratly Islands. Today, the People's Liberation Army and the Republic of China Armed Forces are both stationed in several islands, including the largest, Taiping Island - occupied by ROC. From 1932 to 1935, the ROC continued to include the territory in its administrative area through the Map Compilation Committee. When France claimed nine islands of the territory in 1933, it immediately encountered a revolt from Chinese fishermen and a protest from the Republic of China government in Nanking. After the second world war, China reclaimed sovereignty over the islands from the Japanese through internationally recognised arrangements based on various treaties settled by the Allied Powers (e.g. the Treaty of Taipei with Japan), and in 1947 China built stone markers on several of the islands.
In 1947, the ROC government renamed 159 islands in the area and published the Map of the South China Sea Islands; as such, it was the first government to establish an administrative presence in the Spratly Islands, and it has occupied Taiping Island (the largest island) constantly since 1956.
It is consequently clear that - whether ROC or PRC is the rightful claimant - by the time of the UNCLOS in 1982 these islands were not "terra nullius" and the uninlateral extension of a 200 mile EEZ does not confer sovereignty in the face of existing title (UNCLOS Article 15)
Vietnam does not have a legal leg to stand on