cygpup, free advice is worth what you paid for it! So, I will throw my opinion into the mix. It is "safe" to delete the things that Disk Cleanup presents for removal, but the items that you list are not very big. If your goal is to free up space on the hard drive, then deleting error reports and ActiveX controls ("downloaded programs") will net you very little extra drive space.
Instead, if you are looking to make space, I would suggest that you use a space management tool, such as WinDirStat or TreeSize to find what is hogging space on your drive. Use that to find programs to uninstall, data that can be deleted or moved, and so on. Once you are done manually cleaning up what you can, use CCleaner to remove browser caches and such. Finally, just to be neat, defrag the drive. That doesn't give you more space, but it consolidates the free space and may speed up file access.
Oh, yeah, you should also have a backup of all your important data.