Here's the problem. You want to give your remote users access to the shares and you've instructed samba to allow guest access - which it does. But the underlying linux permissions is only allowing you to read and write.

There's two ways to fix this:
(1) Mount the drives in fstab with the correct permissions if it's a fat32 or ntfs partition. Or a chmod if it's a ext3/4 partition.
(2) Or use samba itself to fix this problem:

Open Terminal
Type gksu gedit /etc/samba/smb.conf

Then change this:
[Drive_1]
path = /media/Drive_1
guest ok = Yes

[Drive_2]
path = /media/Drive_2
guest ok = Yes
To this:
[Drive_1]
path = /media/Drive_1
guest ok = Yes
force user = tonyw

[Drive_2]
path = /media/Drive_2
guest ok = Yes
force user = tonyw
This will create a mask that will make linux think that the remote user is you ( as far as that share is concerned ) since you are the only one who has access to it.

Save the smb.conf file, exit gedit, and back in the terminal issue a : sudo service samba restart