I found the solution to the most common installer error!

IF you are running guild wars and all of a sudden it says can not write file to installation because you need administrative access or soemthing like that, it's because you have spybot teatimer running.

Heres what you do:

Ctr+Alt+Delete
CLick processes in the task manager
click on teatimer.exe and click end process
click yes
run guild wars
Pwn some noobs

Thanks for posting the info, i'm sure a lot of people still don't know about that. However, this solution has been around the forums for some time now, but like some threads in this forum, it can be hard to find.