I originally made this tutorial for amv-argentina forum, but i will traduce it and share it here :) (dont kill me for my english x__x)
Ok, a lot of people thinks that only After effects has a ram preview... but vegas also have it.1)
First you need to configurate the memory that vegas can use for do the ram preview. Go to Options / Preferences / Video
and where it say Dynamic RAM preview (MB) add a value.Important: The value that you add here is the memory that vegas will reservate for ram preview, so don´t add all the memory that you had like a did on the picture xD.. for example if you had 8000mb (8gb) ram, add 1000mb or 2000mb only.2)
Then just sellect the part of the video that you want to watch, and press Shift + B
.. then wait for vegas to process the frames and finally you can press "Play" and watch that part of the video without any lag.
PS: If you add a high value to the ram preview the program is going to be able to process a long time of video. If the value is short.. vegas will process only a few scenes.
Your moment of truth is the day that you say.. i'm not scared!!