Handling 2 internet connections

I currently have a Netgear MR814v2 connecting 2 PCs by wire, a PDA
wirelessly, and an ADSL broadband internet connection coming off a
set-top box which supplies video on demand as well. I now need a static
IP address for work access and the ISP does not offer that facility, so
I am getting a second broadband connection from another ISP, for which
I will need a modem. I will keep the first ISP as well as I want the
video stuff and also it's a useful backup.
My question is what do I need to buy for the new configuration? I want
to be able to use the static IP address most of the time but be able to
switch to the old one simply. Do I buy a combined router-modem such as
the Netgear DG834GT? How do I connect it to the existing router?
Any help gratefully received.
Thanks,
Peter Croft