cisco 803 dial two different corporate networks?

Hi all,

I don't know whether this is possible, but I was wondering if someone could
help me out.

We have a permanent DSL connection to the internet, we use a linux firewall
for that. Most of the remote connections we make are with VPN or SSH to the
customer. We have two customers that refuse any other connection than ISDN
dial-up. At the moment we have to use a PC with an ISDN modem to remotely
connect to both customers. We have a Cisco 803 router which we don't use
anymore. This 803 has one ISDN interface. I was wondering if it was possible
to use that 803 on the network and let that dial to the customer depending
on any kind of action we perform on our (windows) PC. I'm not an expert in
Cisco IOS, but from what I have seen on some sites, is the possibility to
enter two different phone numbers to call. But I'm still not convinced
whether the examples would work for us, because the examples are not 100%
equal to our situation. I have a few questions, that I hope someone can
answer:

Q1. Is it possible to define two different dial-up networks (as in corporate
network) in a 803?
Q2. Is it possible for one of those dial-up networks, to allow a callback to
the 803? At the moment, we need to dial the number on the windows PC, the
device (don't know for sure whether it's a router or RRAS server)
authenticates us, and calls us back. We are then connected to the network.
Q3. How can I tell our own windows PC's to "talk" to our dial-up router
instead of "talking" to the default router (which is the DSL connection to
the internet)? I guess by adding a static route on our windows PC's, but am
I right...?
Q4. If our windows PC's are able to determine succesfully when to "talk" to
the DSL router and when to "talk" to the dial-up router, how can the dial-up
router determine which customer to call?

If we can get this to work, we can free up a workstation again, and reuse
our Cisco 803 router again. We would also make it possible to work from any
place on the LAN to the correct customer.

Our network is a class C network. We use a Windows 2000 Server as domain
controller and RRAS server for incoming connections only. We have a FreeBSD
server which runs the mailserver, and DHCP and internal DNS server.

Thanks in advance,

With kind regards,

Dennis Ortsen