HOW TO CLEAN UP YOUR WINDOWS BOX IN ONE EASY POST:
Boot your machine into safe mode with network support. This should prevent the offending NT Authority thing from starting with your computer.
Install
AntiVir, Spybot S&D, Lavasoft Adaware, ZoneAlarm firewall, and Firefox. Update them all, and install the Firefox extension "NoScript" from the Extensions bookmarked page.
Reboot into safe mode WITHOUT network support and physically disconnect your machine from the internet.
Run AntiVir, Spybot, and Adaware, allowing them to clean up anything they find and deleting infected files.
Still in safe mode after those have run, go to the start menu, click Run, type 'msconfig' into the commandline box, and hit Enter. In msconfig, click the Startup tab and uncheck the boxes for every program you don't recognize, including NT Authority and any DLLs and/or EXEs that have random-character names. This screen should also provide paths and filenames for these programs, so that you know what is what. When it asks to restart, tell it no.
Run Scandisk and Defrag/Diskeeper/whatever to get back some of your lost speed. You'll probably never have a better opportunity.
Reboot into normal mode. Make sure AntiVir Guard, ZoneAlarm, and Spybot S&D Teatimer start with the system. Set your default browser to Firefox and be happy that you now have a relatively clean system.
You may now reconnect to the internet and resume your regularly scheduled programming.