I'm having an issue with latency using:

macbook pro 2.3 ghz, 3GB RAM, 120 GB hard drive
logic pro 8
tascam us-1641 fully updated (1.01 firmware, and 1.0 OS X driver installed)

When I listen to live sound, there's about a 1/2 second delay. I've tried adjusting the adjusting the buffer size to a lower setting (below 256), but then I start to hear wierd noises, or nothing at all. Any suggestions?
Thanks,

CH