基本上Check dma, irq ,power saving mode(acpi or apm-no power saving >apm>acpi),make sure dont compress sound at the same time,delete all background program, install directx8 and dv update( if u use new driver),check which color format is better for ur video card(some card better at yv12, some card better at yuv2, when capture disable both overlay and preview, and check which version is better for ur capture.

if u still got drop frame, try to use microcrap v2 or v3 codec(v2 use less cpu and have better quility for capture).

if u still gor drop frame,hmm, use things like motion perfect to rebuild ur frame(will look like doesnt drop any frame, sign)