Vista startup problem – Documents folder opens on startup. Help?!?

So when i start my computer it brings up the log-on screen and i type in my password and it hangs saying welcome with that spinning blue circle thing next to it and then brings up the documents folder with nothing else but empty blackness. Somewhere I saw an article saying it was a registry error probably caused by a virus and that an edit of this would fix it (cant remember the path). So i tried it by doing something like finding an entry with the value ‘userinit.exe’ (no quotes, and yes i meant to put that comma there) and I restarted my computer and it came up and said it couldn’t boot, ran diagnostics or something and obviously fixed the error. But my main problem remains. explorer.exe does run, but it is not the desktop, it is the my documents folder. It may be running the wrong explorer.exe. These processes are, however, running whilst i am running task manager – ‘csrss.exe’, ‘dwm.exe’, ‘taskeng.exe’, ‘taskmgr.exe’ (obviously while I’m running task manager), and ‘winlogon.exe’. I am pretty sure that this is a virus because on one of my accounts, it brings up a window asking for admin privileges to run a Windows Update file by an unidentified publisher. of course i hit no and then my AVG Free Antivirus asks if i want to move it to my virus vault. if i hit yes, windows will come up with an error message for this file saying it isnt there, so i put it back. Its in a folder like ‘C:UsersAppDataLocalWindows-UpdateKBxxxxxx.exe’ (where the x’s represent numbers). I have made a new account and it took about 2 minutes to create my desktop, then didnt apply the usual transparent theme, but a windows 9x type theme until i hit File, New Task, and typed explorer.exe. then it loaded the desktop. I run Vista Home Premium and i believe i had the same problem on my old pc running XP home premium, but only on one profile. I know that he easiest alternative is a reinstall, but i would like to avoid this if at all possible. I hope that i havent given to much info. Remember that i will award 10 points to the best answer. Also I am considering switching to using a portable version of Linux, if anyone could point me in the direction of a working guide to install Linux on a cd with a live file system, or a usb hard drive, i MAY award 10 points if i do not get a working reply for my original question.
ty for the help, i knew i should have added that, i have done multiple scans with AVG and Spybot S&D, but thanks so much for your help