I need help created a SHARED MAILBOX using Exchange 2007

I have been tasked with setting up shared mailboxes on our Exchange 2007 server. I have already discovered that I cannot use the Exchange Management Console and believe I need to go through the PowerShell. I tried the command below but got the following error. Do you I need to set up a user account in active directory first? We are running Windows 2008 domain level. Am I on the write track with the command below? Maybe I
Just made a typo? All advice welcome



PS C:\> New-Mailbox -Name:'Budget' -OrganizationalUnit:'Domain.com/Exchange Res
ources' -Database:'Mailbox Database' -UserPrincipalName:'budget@domain.com' -Sh
ared
The term 'New-Mailbox' is not recognized as the name of a cmdlet, function, scr
ipt file, or operable program. Check the spelling of the name, or if a path was
 included, verify that the path is correct and try again.
At line:1 char:12
+ New-Mailbox <<<<  -Name:'Budget' -OrganizationalUnit:'domain.com/Exchange Re
sources' -Database:'Mailbox Database' -UserPrincipalName:'budget@domain.com' -
Shared
    + CategoryInfo          : ObjectNotFound: (New-Mailbox:String) [], Command
   NotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException