Thanks to "Mike" for the following information...
General
If you have a Draytek Vigor 2600plus you can save yourself the trouble of making almost all of the 2600-specific configuration changes noted in the help file by using the Draytek2600.ini file in place of the RouterStats.ini file.
To do this make sure that Routerstats is not running, then copy the Draytek2600.ini file into the same directory as Routerstats.exe, delete or rename any existing Routerstats.ini file [there may not be one], and rename Draytek2600.ini to Routerstats.ini. The configuration changes will come into force next time you open Routerstats.
You'll find Draytek2600.ini in the OtherRouters folder included in RouterStats.zip
The login URL for 2600plus is: http://192.168.1.1/doc/online.sht
The username admin can be used together with any password you have set.
Using a blank or space for the username can cause problems with Routerstats. (I think the current help file needs correcting in this respect, as I'm pretty sure this would apply to the 2600G as well).
The 2600plus does not seem to have a logout function.
If your router has a password, you will need to type in a password as described in the help text under 'Configuring RouterStats'.
The 'use source' tick box seem to give most stable results with the 2600plus.
Configuring and using the graphs
The 2600plus does not display an Rx Noise figure on the web interface, but you must map this graph to some router statistic or problems occur in the other graphs. The RouterStats2600.ini file maps this graph to Loop Attenuation.
Graphs and hence alarms and max and min statistics can go wild when the router is rebooting, or re-synching. The facilities Routerstats provides to control this do not seem to work for the 2600plus.
The reboot URL for the 2600plus is:
http://192.168.1.1/cgi-bin/reboot.cgi?sReboot=Current&submit=++OK++
Graphs take 3-5 minutes to settle down after a reboot. If they take longer, the router may be having trouble establishing a full connection.
Additional features:
The 'string= entry' to display the external* IP address for the 2600plus is (counterintutively*):
[IPAddress] String=<font face="Verdana, Arial, Helvetica" size=2 color="#009900"> PPPoA</font> URL=doc/online.sht IPOffset=71*The IP address 'seen' by users on the web or WAN side of the router.
(*the above is the first unique string before the data. Setting a seemingly more relevant string causes RouterStats to pick up the wrong data)
(?Presumably the 'email when IP changes' function will operate if you set the IP string up as above. The user interface suggests this is limited to the Netgear router? I cannot set this as I have a static IP).