(there seemed to be a few categories this could fit into, please correct me if I've put it in the wrong place)

I have an external USB hard-drive that I'd like to share between these devices:
LinkSys WAG310G (I'm using this with Xnet Fusion VoIP) - with USB "storage"
Windows Vista
Mac OSX
Xbox 360
PS3

Our PS3 has been getting some good use for movies and TVNZonDemand lately, and I thought it would be a good idea to put our DVD collection on HDD for easy access.  I'm also very keen to have my music collection on HDD for playing on random through the home theatre. 
I'd like to be able to use the PS3 for this as it's our media centre, and it would be nice if the 360 could access the music for in games.  Both the Mac and PC will need to be able to add files to the HDD, and I'd like to be able to choose a couple of albums each morning to put on my iPhone (via the Mac) before leaving for work.
I really want to (and think it's reasonable to) do this without unplugging and replugging things.

Here's what I thought I'd be able to do:
- Network everything up so they can all share the internet wirelessly (wired in the case of the 360) - so far so good! 
- Plug in the USB hard-drive into the USB port on the WAG310G router, and have each device able to access it for movies and music.  Well, the router detects the drive but it seems that with this router you can only read/write the drive through the router's own web interface, ruling out mapping the drive in Windows explorer, let alone accessing it from the PS3, 360 etc.  Wish I'd known that before purchase!

Is there a way to do what I want with what I already own?  In light of the information above I doubt it, so would I be best to:

- Buy a better gateway/router that allows proper access to the USB HDD? (Keep in mind I'm using Xnet Fusion)
- Buy a NAS HDD enclosure with a network port?
- Or if I forget about the 360, is there a way to have the USB HDD connected directly to the PS3 that still allows the computers (Mac and PC) on the network to access it (read and write)?

Any input/suggestions/opinions greatly appreciated!