I too experience the "lyrics drift" where by the end of the song the lyrics is a good second or two off. Although the time in Winamp agrees with the time on the stamp, the row isn't being highlighted until some small time later (>2 seconds by the end of the track).

I too am using a poor quality onboard sound card -- ESS Maestro on a Dell Insperon.

From Winamp's "Directsound output" status tab (from output plug-in config):
Certified: yes, emulated: no
Supports sample rates from 4800 Hz to 48000 Hz (continuous)
Hardware memory: N/A
Hardware mixing: supported, 15 free streams (17 max)
Speaker setup: stereo

This could be verified by seeing if the lyrics scroll fine using my fancy Soundblaster Audigy USB soundcard at home... I'll let you know this weekend ;-) If not, could it have something to do with the DirectSound output plugin doing [cross-]fading?