If access to an institutional ECN aggregator was readily available (unfortunately, it's not) the best solution for a "tape" would be streaming the best bid via API. http://vcapfx.com/cax-portal-aggregator.asp http://flextrade.com/flexfx.php You could do the same with IB's API (see attachment), but the price changes wouldn't be as indicative of the overall market as the aggregators.
(sighs..) using the Search facility would have unearthed this very recent thread on the same question: http://www.elitetrader.com/vb/showthread.php?s=&threadid=106239