I'm not exactly sure what you mean by "different sequences". You can rearrange the timeline however you want to put things in a different sequence. You can also used "nested VEG files" if you want to include and entire project inside another project. For example, if you have a title sequence you really like, you can just add that PROJECT to your new project to include that title.
The functionality you are referring to is done by using nested projects in Vegas. You can take an entire project and place it on the timeline. You can then right-click the nested project and open it for additional editing.