refresh rate issues

Hello,

I have written a text-based subliminal priming task to be used on some six-year-old laptops running XP. Even though the task is entirely text-based, I am still encountering difficulties getting DirectRT to display the subliminal prime for an acceptable period of time. I have set it to display for 15 ms (and the display tests at about a 17 ms refresh rate), but the log file indicates that these stimuli are nevertheless appearing for at least 30 ms. I have even set the trial interval to 2000 ms. The machines are running clean installs of XP pro, have no active network connections, etc. I have also updated graphics drivers and experimented with different resolution settings, all to no avail.

Is there anything I have overlooked, or is it time to convince our thrifty PI to find some newer machines? Thanks in advance.

--Sam