Skytap is scheduled to flip the switch today on the widgetry that will let developers and enterprise IT departments compatibility-test their Windows 7 applications in its cloud lab.

Users will be able to spin up a virtual sandbox, see if their apps run right on the new operating system and iron out any kinks ahead of 7 hitting the broad market at the end of October.

For a limited time the widgetry will cost $250 a month for 1,000 hours of testing time, a price that includes team access to Skytap’s Virtual Lab SaaS application and Windows 7 virtual machine templates.

The thousand hours might be enough for a single app of relative complexity, senior director of product marketing Ian Knox ventured.

Skytap expects to be alone in such an offering. Other clouds like Amazon aren’t set up to handle the client side, Knox said.

Microsoft, which wants to avoid any of the compatibility screw-ups that marred Vista at all costs, is expected to tout the Skytap service to its developer base.

The 451 Group observes that compatibility testers have to stand in a long line to get a crack at the hardware needed to run their tests. That means critical testing is often left to the last minute resulting in bugs and conflicts. It says that by using Skytap’s cloud organizations can run early tests and gain the time needed to resolve any issues with applications and middleware stacks.

Developers need to test against registry changes, retired DLLs, library dependencies, newfangled security, user access controls and IE8.

Then there’s Windows Resource Protection, XP Mode, version checking, 64-bit architecture and language compatibility, among other things.

Skytap says, as seems logical, that there are more significant compatibility issues coming from XP than Vista since Windows 7 is a remade Vista.

Skytap, which is built on a VMware infrastructure and is supposed to offer 50%-75% TCO according to Gartner, lets organizations use their existing MSDN licenses. Tests can be run in parallel