The query used to fetch the currency information was
http://query.yahooapis.com/v1/public/yql?q...ltableswithkeys

and the result is

<?xml version="1.0" encoding="UTF-8"?>
<query xmlns:yahoo="http://www.yahooapis.com/v1/base.rng" yahoo:count="1" yahoo:created="2011-06-22T07:01:33Z" yahoo:lang="en-US"><results><quote><LastTradeDate>6/22/2011</LastTradeDate><LastTradePriceOnly>44.815</LastTradePriceOnly><Name>USD to INR</Name><PreviousClose/><Symbol>USDINR=X</Symbol><LastTradeTime>2:59am</LastTradeTime><StockExchange/></quote></results></query><!-- total: 449 -->
<!-- engine3.yql.sg1.yahoo.com -->

NOTE: The same query used for stocks (GOOG) and it returned the previous close value

Please help us on how to get the previous close value for a currency?