automounting external hard drive

[Linda Hanigan]

I just bought a 500 GB seagate usb external hard drive. I want to use it
to backup several windows xp laptops and a Ubuntu computer. When it
automounts on the desktop it mounts as readonly. I'd like to change the
automount so it mounts read/write but I don't know where to find the
settings. Also how do I find out what type of file system is on it? It 
is suppose to be mac and windows compatible.
                       Thanks
                        Linda