Your comments are useful - thank you.
I'm afraid i don't fully understand Samba. With Draytek it didn't seem to get installed on my PC when I had it working with XP. I assumed it was in the router software.
I wonder if you could help me with this and tell me where Samba 'lives' please?
From what you say I'd be OK with a hard drive housing with network connectivity (RJ45), and I'd get decent performance with full read/write/update etc. facilities on the drive from a main wired PC and a wireless laptop. Is that correct?
Thanks again.

Samba is opensource software which is an implementation of Windows networking for UNIX.

www.samba.org

The 2820 contains a Samba server. Nothing is needed on your PC, Windows already contains all the necessary software.

If you want to get an idea of how fast a separate proper NAS drive would be try sharing out one of the existing hard drives on your PC and access it from the laptop over your network, speed of the NAS drive will be about the same.

Thanks for your help. I have the 2710, but that must have Samba too, as it worked with XP. I'm now waiting for Draytek's reply to me about Windows 7 problem. I'll post reply when I get it.

Here is the reply about Windows 7:

"Try disabling UAC (User Access Control)" Go to Control Panel, User Accounts, Change User Account Control Settings and pull the slider all the way down.

And this is how I made it work after doing that....

Make sure the USB drive is connected
On any Windows Explorer window (e.g. My Computer): Enter \\192.168.1.1 and you should get your user ID and public as Share folders.
Click the icon and log in with your ID and password. Decide if you want this remembered for automatic connect.

Now Right click the user id icon and choose Map Network Drive. If you check Reconnect at logon you will get a Windows message near the Notification area if you drive is not connected at startup.
If you don't map the drive you can't use it as a normal drive with a drive letter. Most attempts to use file associations from the network entry in Computer will cause the expected automatic program start (e.g. Photoshop for a .JPG file) to 'jam' with Program not responding.

By the way, Draytek's email reply also said the latest firmware for the 2710n is 3.3.5.1 at http://www.draytek.com/user/SupportDownloadsDetail.php?action=Load&MID=10&ID=419 and download 'Annex A modem code 211801' version.

BUT I suspect you need to check your modem code to make sure you get the right download. Go to 192.168.1.1 in a browser, login with blank user name and password, and it's next to your current version at the top of the System Status page e.g. Firmware Version : 3.3.2.2_211801
Perhaps someone would confirm I'm correct about this check...

Meanwhile I'm sticking with 3.3.2.2 as long as it's working