rendering times will also be greatly affected by what is done to those clips. are there a lot of effects applied? is there a lot of color correction? 3-d movement? are the frames having to be resized in any way? Project properties and render properties are compatible or the same? Also, check the program affinity to see how many cores are set to use. Vegas uses the processor and not the video card when rendering. Are you rendering to the same physical hard drive that the media is stored on? You shouldn't be. Do you do regular maintenance on the computer (i.e. blow dust out of case, fans, heat sinks...., hard drive maintenance etc.)  Heat buildup and improper ventilation will slow your computer down too.
If you want to look at using intermediate files for editing, take a look at gearshift (http://www.vasst.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=102&category_id=74&option=com_virtuemart&Itemid=59)
use the intermediates to edit with and when you go to render, replace the intermediates with the original footage. Have fun with Vegas, it's a great production tool. The studio versions are really good, but Vegas Pro will give the the best bang for your buck.
John
