Cisco 877 – How to Use as a VPN Server

I have a Cisco 877 router which connects my network to the Internet using an ADSL line, a single public IP address and NAT; the IOS version is 15.

Everything is working ok, but I'd like to configure this router to be a VPN server, to be able to connect to the network from the outside.

I've tried looking for documentation, but everything I can find is related to having the 877 act as a VPN client, or to site-to-site VPNs; I can't find anything about letting single remote computers access the internal network, which is something I can do quite easily using Windows' RRAS or ISA Server.

• Can the Cisco 877 act as a VPN server for remote client computers? (Looks like it should, but just to be sure…)
• Which type of VPNs does it support? Do they require some special software on the client machines, or can they be used by standard out-of-the-box Windows computers?
• And, finally: how to set up this?

Edit:

I know the 877 is a SOHO router, and it's not the best choice as a VPN server; but this is my home network, I only have one computer (for now) and I'm the only user. I'm definitely not going to buy an enterprise-grade router just to be able to reach my PC when I'm at work :-p

Edit 2:

I'm really stuck with this, after many tests I was never able to get it to work. I'm adding a bounty to the question, which will be awarded to a fully working solution (not to some pointer to cryptic Cisco documentation or unrelated scenarios).

In order to allow people to help, here's my current router configuration (stripped of non-relevant and private details). Let's hope someone finally can help me get this working.

Main points:

• The four Ethernet interfaces are all assigned to VLAN 1.
• Internal network is 192.168.42.0/24, router's IP address is 192.168.42.1.
• External IP address is supplied by ISP; it's a public and static one, fully routable.
• NAT is (of course) enabled.
• ADSL connection works OK.
• The router is the DNS server for the internal network, forward queries to the ISP's DNS.
• There is no DHCP server in the network.
• There is a single user account with privilege level 15.

What I want:

• The router acting as a VPN server, enabling external clients to access the internal network.
• L2TP would be preferred, but even PPTP would be ok.
• If possible, I want this to work with Windows' built-in VPN client (which supports PPTP and L2TP); I don't want to install Cisco VPN client or anything like that on external computers in order for them to be able to connect.

Here's the config:

version 15.0

service password-encryption

hostname Cisco877

aaa new-model

aaa authentication login default local
aaa authorization console
aaa authorization exec default local

aaa session-id common

ip source-route
ip cef
ip domain name <my ISP's DNS name>
ip name-server <my ISP's DNS server>
no ipv6 cef

password encryption aes

username <Router's username> privilege 15 secret 5 <The encrypted password for my user account>

ip ssh version 2

interface ATM0
 no ip address
 no atm ilmi-keepalive

interface ATM0.1 point-to-point
 pvc 8/75
  encapsulation aal5mux ppp dialer
  dialer pool-member 1

interface FastEthernet0
 spanning-tree portfast

interface FastEthernet1
 spanning-tree portfast

interface FastEthernet2
 spanning-tree portfast

interface FastEthernet3
 spanning-tree portfast

interface Vlan1
 ip address 192.168.42.1 255.255.255.0
 ip nat inside
 ip virtual-reassembly

interface Dialer0
 ip address negotiated
 ip nat outside
 ip virtual-reassembly
 encapsulation ppp
 dialer pool 1
 dialer-group 1
 ppp authentication pap callin
 ppp pap sent-username <My ISP's username> password 7 <The encrypted ISP password>

ip forward-protocol nd

ip dns server

ip nat inside source list 1 interface Dialer0 overload
ip route 0.0.0.0 0.0.0.0 Dialer0

access-list 1 permit 192.168.42.0 0.0.0.255

dialer-list 1 protocol ip permit