To convert the price to some other currency we need to select that currency in allowed currency and import currency rates from System->Manage currency ->Rates .
The synatx for currency conversion is currencyConvert($amount, $from, $to=null)
Suppose we need convert Price from GBP(British Sterling Pound) to INR(Indian currency) then we need to write below code .

$convertedPrice = Mage::helper('directory')->currencyConvert($price, GBP, INR);