Must you not have a copy of the full version of your current operating system if you want to perform a clean install using an upgrade disk? So if current system is a 32 bit operating system then even a fresh install using 64-bit UPGRADE disk won't work. :)
Ok, now your statement is a little confusing. Your current OS is a full version (doesn't matter how you got it there), u don't need any copy as you don't want to upgrade to where it is right now.
I think the second part of that person's question states that a clean install would be a good idea but wanted to find out if the option of upgrade was available from where their PC is to where they want it to go.