I am asked to configure a cisco 801 router with the following
characteristics:

- Europe, ISDN connection, network protocol TCP/IP
- The router would be in a remote office, and it would connect to a
central office when traffic is generated from the LAN in the remote
office (Dial on demand Routing)
- IP on the outside interface of the central office C.C.C.C
255.255.255.252
- Phone number of central office 555 5555
- IP on the outside interface of the remote office R.R.R.R
255.255.255.252
- IP on the inside interface of the remote office I.I.I.I
255.255.255.0
- All traffic generated from the LAN in the remote office should go to
the central office with a translated IP (NAT) N.N.N.N 255.255.255.252
- This link is intended to access from the remote office to a telnet
server placed in the central office. The telnet server's IP is S.S.S.S
- Static routing to reach the telnet server and the NAT address
- MTU:1500, Keepalive:8, Encapsulation:PPP
- Only telnet traffic should be allowed to leave towards the central
office

I hope this is enough to build a configuration file.
I would also like to clarify some details about this configuration.
Please, tell me if this is not allowed in the same post, or if it is
considered to be the same request.
-¿Why use a NAT address different than the IP address of the outside
interface?
-¿Why a static route to reach the NAT address? ¿Is it necessary? 

Thanks

This configuration should put you in the ballpark. No need to creat a
NAT pool when overloading the outside interface will work just fine,
and no need for a static route to reach NAT addresses provided your
internal routing scheme is in order. The configuration below will only
dial the router when telnet traffic is initiated to the telnet server
and only telnet traffic will be NATed. Good luck.

!
no service pad
service password-encryption
no service udp-small-servers
no service tcp-small-servers
!
hostname Cisco 801
!
enable secret manager-password
!
ip nat inside source list 100 interface BRI0 overload
no ip domain-lookup
isdn switch-type basic-net3
! 
interface Ethernet0
 no shutdown
 ip address I.I.I.I 255.255.255.0
 ip nat inside
!
interface BRI0
 no shutdown
 ip address R.R.R.R 255.255.255.252
 ip nat outside
 ip tcp header-compression
 encapsulation ppp
 dialer idle-timeout 1800
 dialer enable-timeout 1
 dialer string 5555555
 dialer hold-queue 100
 dialer-group 1
 no peer default ip address
 no cdp enable
 isdn spid1 SPID1
 isdn spid2 SPID2
 dialer load-threshold 1 either
 ppp multilink
!
ip classless
ip route 0.0.0.0 0.0.0.0 BRI0 permanent
access-list 100 permit tcp any host S.S.S.S eq telnet
dialer-list 1 protocol ip list 100
!
line con 0
 password user-password
 login
line vty 0 4
 password user-password
 login
!
end