Microsoft Exchange 2007 Question

Instead of typing I will refer you to this:
http://www.msexchange.org/tutorials/planning-first-exchange-server.html

Can i have MS Exchange installed with DyDNS for Static IP?

It is possible, but really not recommended.
Not recommended at all.
You might want to look into a hosted exchange service, if the cost of a static IP is prohibitive.
How many users are you going to be supporting? Are you only sending outbound mail?

ok, that's what i was thinking, if possible as you say, then how can i proceed as a test?

I think I need:

1 dyndns account
1 domain

The problem is, how can i link my domain and set the NS entries to the dyndns account ?knowing that i can enter the MX entry in the MX data in my domain interface. any idea?

there will be like 50 user Sending & receiving emails from inside and outside the company

For a company that size, I would look at Microsoft Small Business Server.
It will give you the domain you need, it will give you Exchange, and it is the cheapest option as far as getting exchange up and running. You will need to have your SBS server up and running ADDS and Exchange before you can test the Dynamic IP solution

Here is a link from Sembee
http://exchange.sembee.info/network/dynamicip.asp

yes but as you said it's not recommanded

I'll move to google app as you said, thank you