Right. Here's how I would do it, but there might be a slicker way, so see how you get on with it.
I found that it's not too keen to work in user folders (e.g. John Smith), as the gap in the path interferes with either batchfile or the .vbs file.
Anyway, I created a folder in C: called 'saves', dumped them in there, and setup a scheduled task to run it. It worked fine. You'll need to mess with the paths if you intend to save it somewhere specific. Also remember to change the web URL.
This doesn't handle any sort of password or browser access though. This captures a normal website to .mht
To schedule it, open Task Scheduler (All Programs, accessories, system tools). Create Basic task (on the right pane). The wizard is pretty straightforward. Create a dummy task with a 'run once only' trigger for a few minutes ahead, and test it. Once you have a working setup, change the task run to daily / timed etc.