Hi vanwolf,
Thanks for posting your question. I'm more than happy to assist you today. Your OSCommerce store is located at: http://oscart.hobbitscoins.com/
Subdomains are treated almost like separate websites. You can link to it by using the URL above. If you are using the Premium Web Builder for your main website, you'll want to add an external link. Here's our tutorial on adding external links in Premium Web Builder:
Adding External links in Premium Web Builder
If you need further assistance please feel free to contact us.
Thanks!
Tim S