Grace-
1. Try the following command-
static (inside,outside) tcp 25 [public IP or interface name] 25 [IP of Exchange Server] netmask 255.255.255.255
EXAMPLES
static (inside,outside) tcp interface 25 192.168.1.10 25 netmask 255.255.255.255
or using a public IP
static (inside,outside) tcp 69.222.73.15 25 192.168.1.10 25 netmask 255.255.255.255
You'll have to adjust your firewall ACL to allow it through as well-
EXAMPLE
access-list external-interface extended permit tcp any host 69.222.73.15 eq smtp
2. This depends on the VPN config. You're probably tunneling all traffic and then you don't have a NAT/ACL block or something not allowing VPN users to be able to get to the internet.
Hope that helps.