When you were following my tut you haven't used the advance settings in the step 7 of the ubiquity installer that resulted with the installer writting the GRUB to your hard drive instead of your USB.
1. To fix your computer - boot the windows installation CD, choose the recovery console ( select R when prompted) and when in the console (c:\) type:
This should fix it. (For XP)
2. The USB - you can repeat the tut from the first post and pay attention in step 7 of the installer to point it to install the grub on the USB, or you can use --grub-install as described in this video
And remeber, you can't follow half a tut and leave out the things you don't understand. Or you can and then mess up your machine.