I have my Mac set up with a personal account for me and I enter my password when I log in, but if I want to lend my computer for someone else to use is there some way I can let them use it without giving them my password? And can you do the same sort of thing with Windows machines?
I will never just lend my computer to anyone, even my friends. Not that I think they will steal sensitive information, I just don't want to risk accidental data loss and that can happen.
Both Windows and Mac's have a "Guest" concept. You can allow your friend limited access on your computer but it will secure your sensitive information. In Windows go to your control panel and Manage User Access.Find the Guest Account and make the account active.
Also add a password (make it different from your password). Now when your computer starts up there will be a choice to log in as yourself or as the guest.
On the Mac you set up the guest account by going to Apple, System Preferences, Accounts, select the guest account and turn it on. .
When your friend is done, you can turn the guest off if you don't want the extra icon at login time. If you decide to leave the guest feature on be sure to add a password to the Guest account. Read the details about using the Guest feature. It may take an extra couple of minutes allowing the user to be changed but it is well worth it This is especially true if your computer is also your company's computer. You do not want your friend to have any access to that information.