A: Technically you can store your screwcapped wine anyway you like. The reason why wine was traditionally stored on its side or inverted was to keep the cork 'moist' - with the porous cork absorbing a little wine on the contact side, thus expanding the cork volume and allowing for a more airtight seal.
Screwcapped bottles don't require this and so can be stored in any position. A word of warning though, be careful when handling screwcapped bottles and avoid stacking them too high - they may look sturdy, but a well placed knock on the side or top can dent the cap and break the perfect seal! (It's happened at Winemakers Choice HQ only recently - I dropped a bottle and dinged it, thought nothing of it, then opened it a couple of weeks later and the wine was oxidised).