Okey dokey matey, not gonna reveal all the secrets to you straight away, will first suggest, if you ever need to forward ports from a hardware dsl router eg. netgear dg834 then best thing to do is rtfm then check out www.portforward.com, all shall be revealed!!
With the point you made about the email requests going to the seperate IP then this is also possible as OSI model will dictate.
-HTTP requests (port 80) will be forwarded to your webserver
-SMTP requests (port 25) will be forwarded to your email server
To achieve these goals you will need to liase with your isp to update their DNS records and add the ip of your webserver to your domain name. Then also asks for the Email (SMTP) requests to be forwarded to the ip of your email server. done diggy done.
