Question : Exchange Server requirements

We are a little company of 15 employees and using POP3 and IMAP email.
Now we want to check the requirements for running an own exchange server in House.
Common Know How:
Exchange Server 2010 Standard License and Hardware is avaiable
Windows Server Know How

Questions:
Is it possible to host more than one domains with the standard License? We have two companies with different employees.
If yes how can we manage the mail boxes - I know that the exchange mailboxes will be configured in AD - do we need a own little Windows Domain?

I heard that there are more than one fixed IP Adresses are needed?
Why? For what? We still run a Terminal Server and we can connect to without problems.

What are more requirements from the infrastructure view?

Answer : Exchange Server requirements

I believe exchange doesn't really care to much about how many domains you have, i think the main differences between standard and enterprise are how many storage groups you can have. Mailboxes are managed from within the exchange management console, you do need to have AD deployed and you usually always need static IP's for servers.