"you need permission to perform this action" on network folder

Greetings,

I am having a problem accessing folders that I made on a newly
purchased external HD set up on my home network via a wireless router.
I set up the HD (a 500GB drive in an USB enclosure) and formatted it
using the Computer Management tools in Vista. It has 1 primary, active
NTFS partition. With the drive plugged directly into my PC by USB, I
was able to format the drive and create two folders at it's root;
'Archive' and 'Restore'. I want to use these folders to hold copies of
my files and back ups of my laptops drive using the Vista Back Up and
Restore tools. I have the HD connected by USB into my ASUS WL-500W
wireless router. I can see the drive (named 'Portable') and the
folders in the Network view of Windows Explorer. However, when I try
and create or copy folders on the HD over the network I get errors
such as "you need permission to perform this action". When I check the
Properties/Security tab of the folders the 'Everyone' user doesn't
have the proper permissions, so I assume this is the problem, but I'm
not sure how to set this. Everything works fine when connected
directly to my PC by USB, but not over the network and I would like to
be able to leave the drive connected to the network so that it's
easier to schedule back ups and gather/deposit/share files with other
users on the network.

Does anyone think there is a solution to this?
Would it be my router settings that are causing the issue or
permission set my Vista, or a combination?

Thanks for the help.

Daryl