"Can you explain why having one account as an admin is trouble? I don't understand that."
It's a very good question.
Here's the scene. You have one single Admin capable account and use that exclusively when you use Windows. Then, suddenly, something happens to that account and you cannot log in to windows to try and fix it. That 'something' could be a malware attack, or a simple "Profile Corruption", which happens more often than we might think.
Without access to Windows, your options become very limited and often that means resorting to a complete reinstall of Windows.
However, with a 2nd Admin capable account, at least you have a chance of sorting the problem out by logging in to that 2nd account and seeing what can be done.
We are now seeing this in Windows 7, but at least with that new OS, when you load Windows for the very first time, you are forced to create your own account and the startup account that allows you to do that then hides itself. But even then, access to the hidden start up account is disabled by default.
But with Windows XP this was a common occurrence. No other Admin account was created and when the only existing account became corrupted, nothing further could be done. The misery it caused was very sad to see.
I hope that explains it.