look at the mount command. I think if you make a directory under mnt call usb the command looks like this:
mount /dev/sdaX /mnt/usb
where X is the scsi drive is gets mapped to. Check the file /var/log/messages as you plug it in. With IDE type drives the mapping should be device /dev/sda1
I don’t have my key with me but from memory that should do it.
In the first few lines you will find one which reads
default=0, in your case it may say 1, 2, 3 or whatever it will be a number.
Below this are the operating systems which are bootable, it is easy to see which is which.
Just change the default= to point to the Windows partition, beware the first bootable operating system is 0 (zero) not 1.