I install as SMESERVER ( Email SERVER ONLY )
SMESERVER - LAN1 -> ISP1
Now i want add a Backup ISP
Can i Add LAN2 -> ISP2 ?
Our Mail can Both run Message -> ISP2 -> LAN2 -> SMESERVER ?
                              Message -> ISP1 -> LAN1 -> SMESERVER ?
MX Record i config  1 & 2 IP to SMESERVER
Wilson,
Your question is a bit unclear.   Do you want a backup mail server or a backup WAN?
1.  If you want a backup mailserver, there are several services available.   I would recommend 
www.easydns.com.  The easydns.com service includes a backup mail server option.
2. If you want a backup WAN (or ISP) connection, then you need to look a deploying a gateway/firewall that provides WAN failover.  SME does not do this.  I recommend pfsense for this:  
http://www.pfsense.org/Greg