There are several ways to do this. One way is to add the following line to your fstab file.
/dev/sda1 /mountDirectory vfat noauto,user,rw 0 0
If you do not know where this file is located, it is in the /etc directory. There are many parametes that you can change, this is just an example. This is also assuming that you usb drive has a fat32 partition type. Most of them do. You will not have to "format" it for linux if you have fat32 support in your kernel. After adding that line, you need to create the mount directory. You also need to make that directory readable and writable.
To mount the drive you then just type in a terminal
And to unmount
The drive will then be mounted in the mountDirectory you created.
As far as copying the linux partition with dd, I don't know exactly what you are trying to copy. Are you trying to copy the boot partition for dual booting with windows or something? You might try
dd if=/dev/hda1 of=/mountDirectory/linux.bin bs=512 count=1
I hope this helps.