I'm looking into purchasing a template for my web store.
Are there any advantages to purchasing a Joomla template vs lets say a magneto template?
For example, if I choose a Joomla template I'm assuming I can use Joomla to administer the store/site.
But what happens if I chose a magneto theme? How would I administser that? Is it easy or hard for a newbie to do so as I am trying to learn.
Joomla is a content management system. Joomla isn't a very good eCommerce platform, but there are plugins to integrate Joomla with other platforms including eCommerce as well as some limited eCommerce plugin solutions. Magento is an eCommerce platform and not a CMS. It is made to specifically handle retail websites.
They both have administrator back ends. Magento isn't too difficult to use. I would say Joomla is easier to use for what it does, but more difficult to integrate a true, professional, full featured eCommerce setup. But if you're looking to do an integration with Joomla I would say it's easier to just use on product rather than two separate products and trying to integrate them properly.
Rockettheme.com has both Joomla and Magento themes that match if you are looking to do a combination of both.
If you dont know how to handle Joomla site, try to purchase Joomla template bundle (usually template + extensions) which is ready to install and setup. This way you can get all in one, but for this I advice you to hire someone.
By the way you are asking the questions I highly recommend you look into a hosted shopping cart provider or to hire a web designer to build a store for you.
Joomla and Virtuemart really is not that great however works well if you want to have other features in your site outside of a store. If your goal is to simply build a store Joomla is not your answer.
Magento is very robust however for most new users it takes time to learn how the system works. Once you do it is very powerful however make sure to monitor loading times and you may need to upgrade from shared hositng sooner than you might with another cart.
Presta Shop is a good answer for a simple store. Be sure to also check out Tomato Cart and Open Cart, newer players with good products.