Thanks for all suggestions. I was prepared to start reducing the size of the ASIO buffer, but decided to play the same song as yesterday before I changed anything and now there is no detectable latency. So now I'm double perplexed. I guess it's possible my computer was being consumed doing something else which caused the noticeable latency. Anyway, I know what to try if this happens again, my M-Audio interface to the ASIO driver allows the buffer size to be changed from the current value of 512 down to 384, 256, 128 and 64.

Matt, yes this is one of the old M-Audio 2496 cards, and I love it too. This is the second computer I've used it in, it just keeps ticking along. This machine is windows 7, a Dell with 2.4G quadcore, so it's always been more than adequate for the things I do. I plan to use Windows 7 until Microsoft stops support in a few years.