Create a new vlan interface and assign it a security level between your outside (100) and inside (0).
int vlan
name-if
security-level 50
ip address x.x.x.x m.m.m.m
Then assign port 4 to the new vlan.
int e0/4
switch acc vlan
Add nat to get to the internet
nat () 1 0 0
Depending upon your license you may also need this under the vlan interface.
no forward interface vlan