I'm working on building my demos for my upcoming Virtual Earth webcast. There are two SDKs for Virtual Earth. The first is the Virtual Earth Interactive SDK. I like what the team has done with this SDK. It is a nice way to get started fast, but when you really want to dig into the APIs, you will probably end up using the more comprehensive Virtual Earth Map Control SDK.
While going through the SDKs, I found myself wanting a version that isn't browser based. I prefer to have a local sdk file over the browser based option. To me, it's just easier to navigate/use. The good news is that the Virtual Earth Map Control SDK is available for download as local Compiled HTML Help file (.chm). You can download the .chm file here.