Cisco Infrastructure :: NATing With Router 1800

I have the following network connected and configured to a single Cisco 1800 router.

VLAN 2 (10.1.20.0/24)
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int vlan2, ip address 10.1.20.1
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 Cisco 1800 ----- int fa0, public ip address ---- Internet
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int vlan3, ip address 10.1.30.1
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VLAN 3 (10.1.30.0/24)
 
VLAN 2 is server vlan with a webserver.
VLAN 3 is clients.
 
NAT configuration:
VLAN 2 and VLAN 3 is using NAT to access the internet, and both is configured as inside interfaces.fa0 is configured as outside interface. Now I don't know if this is about NAT, but I've tried several things without luck.
 
Problem:
A client in VLAN 3 tries to access a domain on the webserver in VLAN 2.It starts by sending a DNS query to a DNS server located at the ISP, and gets the ip address for the domain, which is of course a public ip address. Then nothing happens because the client tries to access the domain on the webserver using the public ip address, and the webserver have a local ip address 10.1.20.20 which is on the local LAN (VLAN 2).
 
I've tried NAT because I have to change the destination ip address, but I can't seem to get it right.