Render to new track is similar to render to DV-avi in terms of render-time. First you invest time to render part of your project and you gain time when you do the final render of your project.
Nesting means that you import your projectfile into another project. Thus save and close your project, open a new project and drag your first projectfile from the explorer (or from windows explorer) onto the timeline of the new project. You will obtain one videotrack and one audio track, which contains the whole project. It does not involve rendering, so it is very fast. However, you will still need time for rendering during the final rendering of your project.
Theo