When asking for username and password the default username is wrong

Question

I have had a look through all the posts here but I can't find anything that helps me. I don't want to actually change my username or reset my password. I know what they both are; however...
I have a recently had to replace my hard drive and now have a fresh install of Snow Leopard. When installing programs the typical enter username and password box pops up but the default username which is populated there is wrong. I have to change it every time before I enter my password. I don't know why this is happening all of a sudden.
For example my username is xxxxyyyy but it comes up as Xxxx Yyyy (note the space). If I enter my password without changing it it gives me an error. If I enter it correctly everything works fine.
This is more of an annoyance than anything. Where/how do I change the default username that is entered into that box.
Any help would be much appreciated.

Answer 1

I was able to change the default account login on my mac --
Go to System Preferences => System => Accounts & click on the lock to make changes.
Highlight the account you want to change & click on the Password tab on the right.
In the box that says Full Name type in your name the way you want it and hit enter.
Reboot you mac.
Your changed name should now be listed as default.
Rick