If you're asking if rendering a longer project is more stressful on a drive that a a shorter one, no, not really. Ideally you should periodically defrag your hard drives so that files are as continious as possible. If you rarely or never defrag your drive then all the extra work the write and read heads need to do can be a little stressful on the drive. Ironically, defragging is probably one of the more stressful things your hard drives does since nearly every sector is going to get read and rewritten and moved, likely several times. However if you rarely or never do it then in time nearly every read/write operation will be to collect file bits scattered all over your drive due to a lack of defragging which in the long run is more stressful.
Actually rendering a long project (assuming your drive is in good shape and not badly fragemented) your hard drive is just loafing along with the read/write heads just gently stepping along. While you'll see the access light blink you shouldn't really hear the drive churning away which is what you're hearing when the read/write heads are jumping around or when your swap file in being accessed excessively.
I've had projects go for 10-20 hours or more rendering already.
Billy Boy, does the amount of RAM have much of an effect on the render time or is it entirely software dependent? I'd check the FAQs but I am rendering a 1.5 hour show and this 1.4 is so sluggish my characters appear after I type them ontimes. This PC is further hampered by being out Internet connection, son's game repository etc.
More memory beyond a certain point isn't helpful for Vegas. I would suggest at minimum 512 MB, 1 GB better. Beyond that problaby not UNLESS you do a lot of RAM renders. I don't.
The biggest thing that impacts rendering time aside from the complexity of the project is raw CPU horsepower. The faster your CPU the shorter your render times. So everything else being equal if you have a project that takes x hours on a slow 1GHz system and upgrade to to a 2 Ghz system it will roughly show a 80% increase in performace at least based on what I've seen. I started with a slow 400 Mhz PII. Vegas running on that was painfully slow. Over the years I bumped up to a 1 GHz, then a 1.5 GHz, a 2.2 and now a 2.8, overclocked to 3.3 Ghz and the decrease in rendering times is pretty constant.
What is installed in your system, son's games, lots of files, etc.. doesn't impact unless you start to multitask. (try to do multiple things at the same time) then too the horsepower of your CPU, the version of Windows you're using and how much RAM you have becomes more important.