Microsoft SDK 5.1 - What is it?

It helps me dictate by voice or speak out text (text to speech)?

Is it included in Windows XP? Which version?

Is it included in Windows Vista? Which version?

I took a look at Microsoft website and found several files to download (some are several MB and one file is 266MB) - Which file should download?

Microsoft SDK 5.1 - What is it?virus removal

It is not included with any Windows Packs. You have to download it or buy it. There are different types of SDK, because there are SDKs that have fewer words than others. My advice is that you should download the biggest SDK you can find...