Windows 7 Enterprise, 90 day trial

* Windows 7 Enterprise 90-day Trial, 64-bit (2.9 gb) .iso

* Windows 7 Enterprise 90-day Trial, 32-bit .iso

Windows Server 2008 R2 Evaluation Virtual Hard Drive Images for Hyper-V (180 days trial)

* Windows Server 2008 R2 Enterprise Evaluation (Full Edition) (2022 mb) .vhd

* Windows Server 2008 R2 Enterprise Evaluation (Server Core) (706 mb) .vhd

Windows Server 2008 R2 Evaluation ISO (180 days trial)

* Windows Server 2008 R2 (.iso)

Good for running inside virtual machines.

Maybe someone can link to these from the Lunarsoft wiki too.

If you're a student (high school or college) you can get Windows Server 2008 Standard (and a lot of Microsoft development tools) for free from DreamSpark.