Right now our internet connection:

Connection type: Leased Line
Router: Mikrotik router
No of Switches: 2
Wifi router: Belkin

In mikrotik router 1 port is used for Input and two ports are used for output( LAN + Wifi connection), so final gatway is mikrotik router.

Leased Line connection gives us sixteen static IP(13 available to use) and we(eight people + 1 server) all got static IP, every thing is working fine.

Now we wanted to change our connection to Broadband since Leased Line is costly. The thing with broadband connection is we won't get static IP. We got one broadband connection also, the guy who give us broadband connection said that mikrotik router won't be connect to broadband connection directly as Leased Line connection does. Broadband connection cable will connect directly to Wifi router and then from Wifi router to Mikrotik router to avail LAN connection. I tried to connect Broadband -> Wifi -> Mikrotik -> switch -> system, after this setup I don't get internet connection for my system I guess I need to change IP address of mikrotik router would get me internet, but I don't know what IP should I use to set Mikrotik router's IP. I checked in belkin router it doesn't show mikrotik router as DHCP client in client list so I don't get IP from belkin router where I suppose to get IP from.

What I want to know Is: Can't I connect mikrotik router with broadband cable directly?
Is mikrotik router good with broadband connection?

Yes the MikroTik is a very good solution for broadband internet. You can even connect both your leased line and your broadband connection the mikrotik at the same time and split the traffic however you want to.

The MikroTik is extremely flexible however it is also very easy to configure incorrectly. In a nutshell you will need to configure your router to connect to your internet provider(s) and to connect to your local network. Then you setup a src-nat rule with the action of masquerade for any traffic leaving your network. If your using multiple connection then you will want to have a default route for each connection that has a routing mark related to that connection. Then you will want mangle rules in the prerouting chain that matches the internal traffic that you want to go out a specific connection and add a routing mark to that traffic. This way you can control the outboud traffic. The inbound that you originate from your side will return properly due to the masquerade rule. For any traffic originating from the internet destined to an internal computer you will want to create a dst-nat rule that will "port forward" the traffic to the internal computer.

I have posted another question, check this out http://forum.mikrotik.com/viewtopic.php?f=13&t=83329