Yes, this is certainly doable
To place the vertical store window in your blog, select the "Edit Store Window" option under the "Store" tab within your Auctiva account, check the radio button next to "Vertical", and click the "Save Changes" button below. Then, click the "Store" tab once again, followed by the "Store Window HTML" link. The store window code displayed on this page will then reflect the certical orientation. Copy this store window HTML code and paste it onto your blog page.
To make the store window retain it's horizontal orientation in your listings, log into your Auctiva account once again, click the "Edit Store Window" link under the "Store" tab, select the radio button next to "Side Scrolling Window" and save your changes. Then, any listings posted thereafter will contain the horizontal store window.
I hope this information proves useful. Please let me know if I can be of further assistance.
-Mike