There are a number of ways that you could accomplish this one.

1 -- You would need to set up a router to route traffice from your 192.0.0.0 network to your 210.0.0.0 network and vice versa. This could be a windows/linux based server with RIP or some other routing protocol set up on it. Or you could go with a dedicated hardware router, these can be more expensive though.

2 -- You could set up a central file server to host all of your files as well as your printer. This machine would have two NICs in it, one with the 192.0.0.0 address and one with the 210.0.0.0 address. That way both networks could communicate with the server.

In order to get both networks to access the Internet, you would need to go with option 1. This is the only way without using a proxy, which I think ISA may do. ISA may also do the filtering that you are talking about.

This was just a basic explanation, so let me know if you need any further explanation.

Andy