You need Visual Studio 2012 running on an x86 or x64 Windows 8 system to do Windows 8 Store application development. If you install VS 2012 on a Windows 7 system you won’t get any Windows 8 components. I asked at Build 2012 but the VS guys said that Win 8 development will never be supported on Win 7, except in a Win 8 VM running on Win 7. You can install the free VS 2012 Express version. Alternatively for development purposes you can install VS 2012 Professional or Ultimate as a 90 day trial. If you then register it you get a further 90 days (180 days in total). VS is also available through MSDN subscriptions.
You can develop a Store app in Visual Studio and test it directly on the development machine. Alternatively you can run it on an emulator on the system which is useful for testing the app in different contexts (eg rotated). Finally you can run it remotely on another system. This is, in particular, necessary to run it on an RT Surface as you can’t run Visual Studio there. When the app is fully developed you normally publish it to the Store for others to get it:
To make an app available to end users there are two options:
Apps published in the Store have the widest audience. This model suites the Indi developer and would be the mode for games and other consumer apps. To publish to The Store you need a developer's license which costs about $US100 for 12 months of activity. In Store apps can be sold through The Store or offered as a free (trial version) with the purchase being directly handled by the software vendor. Signed receipts purchased from The Store can also be used for Volume Licensing of a Store app. As with Windows Phone, apps submitted to The Store are tested against the certification tests, repackaged and signed.
The second option would be for when the app is meant for a restricted audience such as when it is a LOB application or for enterprise software purchased directly from the ISV. Direct installation of non-Store Metro apps (called sideloading) is only available for Windows 8 Enterprise and Windows 8 Server editions (although other PCs can be configured for this. See Deploying Metro style apps to businesses) Apps distributed in this manner should be tested using the certification tests, packaged and signed by the vendor or enterprise that is going to use it. The onus upon their IT to enforce this process and validate it.
You can be licensed as an individual developer with one account for submitting apps. Alternatively a company developer account can be created:
Individual accounts don't require the same verification process as company accounts, but can't submit desktop applications or submit apps that can use the enterpriseAuthentication, sharedUserCertificates, or documentsLibrary capabilities
A company account can use the enterpriseAuthentication, documentsLibrary, or sharedUserCertificates capabilities (See App Capabilities). This means that apps meant for an enterprise that are published in The Store can only be done with a company developer account. It's also the only way to submit desktop apps to the Windows Store. Desktop apps are only listed in The Store with the enterprise hosting its download. The app is still tested before it is approved for listing.