I installed Win7 a while ago, and now I'm wondering if there is no sidebar in Win7? I can't find it, running "sidebar" (win+r) doesn't find it. It's not in the processes either. Is there a way to install it?
Right click your desktop and select Gadgets to add or remove them.
A quick Google finds a way to reinstate the Sidebar but as it is a kludge to copy the files from Vista I wouldn't recommend it.
EDIT: Just reread your question and a thought occured to me... if you have no sidebar.exe (and therefore no access to gadgets via the right click, MS didn't rename their gadget executable from vista and so it is still sidebar.exe) then it could be that the gadget framework is disabled. Go to Start -> Control Panel -> Programs and Features -> Turn Windows Features On or Off. Near the bottom of the list you will find Windows Gadget Platform, which may need to be enabled but as I stated they will be desktop gadgets rather than the sidebar.
Right click on the desktop and click on Gadgets. There is no actual sidebar in windows 7, but it still runs sidebar gadgets. (and the process is still called sidebar)
If you wish to have a sidebar in Windows 7 or 8, you may have it in the form of MetroSidebar - The new generation of Windows Sidebar.
Operating system: 32- or 64-bit version of either Windows 8, Windows 7 or Windows Vista
Installed Microsoft.NET Framework 4
Processor: 1 GHz or higher
Memory: 512 Mb of RAM or higher