here are two useful papers.
older by GS:
http://www.ederman.com/new/docs/gs-volatility_swaps.pdf
newer by JPM:
http://pcj-gonfroy.com/PCJ_GéRant/09 BaR/VarSwaps.pdf
older by GS:
http://www.ederman.com/new/docs/gs-volatility_swaps.pdf
newer by JPM:
http://pcj-gonfroy.com/PCJ_GéRant/09 BaR/VarSwaps.pdf