This link href="index.php?page=account.index&option=com_virtuemart" seems to be the link for maintenance of your account after you've logged in, rather than to a nice login script.
I made my own solution to this. My solution:
1) Create a new menu called 'hidden' with one menu-item called 'log-in'. Set the associated module to show in no menu-items.
The page for this menu-item should be one with no content. It will be your user's login page.
2) Use the Virtuemart login module, but set only to shoe on the log-in menu-item, in a position of your choice (I suggest below the main content).
3) the href you need for your login button is now just the log-in menu-item page. (I'm using SEF on my site so for me it's BASEURL/log-in.
HTH,
Mike
Yes, that link takes you to the "maintenance" area and guess what happens if you are NOT logged in? It prompts you to login!
The solution you suggest makes no sense to me, and it won't be natural to most people, because once you log in you will have to go back to a page to log out. Let me repeat that guys: to log out you need to go to a page and click and extra button. You will realize about it out sooner or later, if you haven't, as I have done it before too. I will also be customizing the PHP file for this page so there is a registration area besides the already-existing area.
The best about my solution is that the login link turns into log out when you are, well, in. Try to do that with the module way (you can't). When I started working with VirtueMart this was the best option because I could do it but as I grew as a web designer I realized this was not a good way to do it from a well-designed-website stand point.