Advice on site to site connection and internet access

We currently run an isdn link between 2 sites (usning nt remote access) as
well as 2 standalone machines at each site with unmetered dialup internet.
This is very expensive compared with 2 adsl connections. A couple of
questions:

I intend on using win200/2003 sbs to handle the internet access to all
machines at the main site using isa.

Do I let win server handle the routing/firewalling etc.. through a second
nic connected to a router in non nat mode. If so do I need 2 public facing
ips to do this (once for the 'modem' the other for the server nic), if I do
this with say a solwise 715 can I also use some of the hardware firewall
features of the router (such as port blocking etc..). Also then running a
vpn server on the windows server.

Or

Plug a router into the switch and let it handle internet access and
firewalling as well as the vpn server. This is the setup I use on my home
network with a solwise 715pv. I think the win server option is probably more
secure and flexiable.

At the remote site we have 2 machines one for accessing network stuff
(currently over the isdn) the other for internet (currently via dialup). Is
there a cost effective way to give one machine a vpn connection to the main
site and the other firewalled internet access. I think the easiest way for
this is a vpn client on the network machine with a software firewall, and
the other machine just connected to a router with a hardware firewall and
possibly a software firewall. (I realise that routers like the solwise don't
offer a true hardware firewall, but rather run their own software one)

What ADSL package should we use for each site, I was going to use something
like the plusnet adsl home 500 package that I use at home as it seems
reliable and offers all the features we need as well as being cheap ~ £20 ex
vat, however I am told that this can not be used for business connections.
The plusnet business account thats £5 per month more expensive doesnt seem
to offer any aditional features apart from being more expensive (are
business customers being ripped off). So can some one recomend a decent adsl
package that can be used for business. As the company is small and they
already cope with some downtime on the internet access and data link, leased
line like relaibility ins't needed. Cost is important.

Many thanks

Jaime