I have an old notebook were I have installed Windows 10 for testing purposes and I couldn't make the Windows Sidebar load. I tried both 8GadgetPackSetup.msi and Desktop Gadgets Installer without success. It loaded for 1-2 seconds and then quitted automatically without even showing something on screen (I watched it through Task Manager). I discovered that the reason was low memory. Apparently the original 512MB memory wasn't enough to load the Sidebar. When I replaced it with 1GB RAM it loaded without any problem.

Conclusion: Windows 10 (and 7 and 8) can work with 512MB RAM (minimum I have confirmed was 384MB) but to use all features, one must have at least 1GB as is the official minimum requirements. And remember that you cannot do a clean installation with less than 512MB (it works with 384MB after installation has completed with at least 512MB) and you cannot make an upgrade from a previous version with less than 1GB (it works with less after the upgrade has been done with at least 1GB). So don't get angry when Microsoft requires at least 1GHz CPU and 1GB RAM. It works for less, but it is too slow to bear!