Most OS's provide some facility to provide user input to an application. This functionality is part of what will get hooked in any decent keylogger and so any means of creating input to the program will likely end up being picked up. This is true whether you use scripts, on-screen keyboards or the physical keyboard itself.
Now, a little good news, some OSes, including Windows when UAC is on, will not share keypresses with non-admin processes, however, if the key logger is running as an admin program, all bets are off.
Short of direct memory injection, you aren't going to be able to get information in to a program without going through the input channels provided by the OS and that's exactly what keyloggers are designed to monitor and pull data from.
Unfortunately, there are actually some pretty good usability reasons to maintain this kind of functionality (such as enabling background processes to respond to shortcut combinations) so it isn't likely to go away any time in the near future. This is part of what makes protecting against key loggers so difficult.
That said, as long as it isn't also logging mouse clicks and positions then you can do some things to confuse it. Making a series of mouse selections to remove content from the string and filling it in will help obscure it a bit, but I still wouldn't advise using it as a protection as it greatly limits the number of possible passwords so brute forcing becomes much more likely.
The best bet is really to change your password to something you can discard and login with that, if you don't want to burn your current password. If you aren't domain connected, you can also back up the user profile files, reset them to something else (this will lock all encrypted files, but that's why you have a backup of your user profile), and then login with the reset password on the new profile. If you have an account recovery disk, using that may also be an option as I believe that does a direct input that would bypass the keypress system. (This is, of course, assuming you are on Windows.)