Hi, Danny
You need to do DNS-Doctoring in order to access the internal servers. This will work only if the internal clients use the server's domain name, not the translated global IP address. Take a look at the following document, it will help you understand DNS-Doctoring:
-- Understanding the alias Command:
http://www.cisco.com/warp/public/110/alias.html
Now, the alias command is very old and is not supported by the PDM (in case you use it), so use the following instead:
static (inside,outside) server-global-ip server-local-ip netmask 255.255.255.255 dns
Hope that helps! Regards,
Federico Rodriguez