How does GAG Graphical Boot Manager work ?

I am trying to use this software but it doesn't seem to work like I expected or maybe I am not using it correctly
I have dual boot windows 98 and XP so at the moment I am using the windows xp boot manager
Maybe if I understand it better I can figure out how it supposed to work
Can I use GAG if I am already using the windows xp manager ?
How does GAG know which OS to load ?
On the GAG menu when I want to add an OS it just shows the OS type but how does it know where it is located on the disk (partition0-1, disk0-1 etc...)?
Right now after I select an OS and I click on it it just takes me to the windows xp menu so this is useless since I can do that without the software