Trying to change Admin. password and name on Macbook Pro... not working, help please!!!!?

Ok, i purchased a Macbook Pro a couple days ago. This is the first mac that i've had, so i'm new to all of this stuff. The problem i'm having is everytime it asks for my administrators name and password, it says that the one i put in is incorrect. So i tried to fix it by using the OS X disc. I loaded it, clicked "Utilities" and "Reset Password"... that's where i run into the problem. The only listed name is "Administrator (root)". Even if i click on that, it says that the name is invalid. I tried deleting the name and adding a new one, but it won't let me. I'm getting very frustrated because i can't install programs... which leads me to another question...

I have installed Limewire 3 times. Everytime i restart my computer, when i click on the Limewire link in the dock, a question mark pops up and it won't open. It did this to me with my Microsoft Messenger too... why is this happening?

If someone could please answer those two questions, i would greatly appreciate it!!! So far, I love my Macbook, but these two issues are starting to get on my nerves. Thanks again!!!