need a little help on cisco soho97 multi ip on solo ethernet

(i'm french sorry about my english speaking) Hi!
I've got a soho97 router. i want to do this :


                                              only int eth0                          my WAN IP 82.x.x.155        
/--------------------/                    11.2.0.201                                         ISP WAN GATEWAY 82.x.x.254                
/     my LAN         /                255.255.255.248                                               255.255.255.0
/    11.2.0.0         /<--------->/CISCO SOHO97/<----------->/MODEM ADSL/<--------------------------->/WAN internet/        
/ 255.255.255.248/                  
/--------------------/

My question: how can i configure my soho97, with this two ip (i.e LAN 11.2.0.201 and WAN 82.x.x.155) on the same ethernet interface??

for further informations about SOHO97 go to :  http://www.cisco.com/en/US/products/hw/routers/ps4866/products_data_sheet09186a008010e5c4.html

I can't use ATM interface (it's working well, but i can't use Phone and TV services), that's why i have to use ISP's modem.
I tried to configure subinterface, but i can't put an ip address (error with ISL and VLAN conf).

I tried to create on "int eth0" two ip adresses, (primary and secondary), but how to configure route and nat translation?

I spent two days to find an answer, and nothing serious about my question, on french forum or website.

So i hope to give you all you need!

Sorry about my english....lol

Merci beaucoup!

Au revoir!!

David