Hello Dushaune,
Basically integrating means that you are going to change Message Store also known as the partner server (Exchange 2k3) to the new partner with Exchange 2k7. For this there are several steps:
-OAB and Extending AD schema
- PW (Permission Wizard)
- MSCW (Message Store Configuration Wizard)
You need to follow this mandatory steps on the guide:
Configuring Exchange 2007 for Cisco Unity & Extending the Active Directory Schema for Cisco Unity
***Even though on the title you see unity 5.x this is still applicable for Unity 7.x, on the documentation guide you will read:
Note 
The following link goes to a Release 5.x version of the guide; all 5.x content applies to version 7.x as well.
On the Exchange side make sure you meet the following system requirements:
Minimum Service Packs Required—Message Store
•Exchange 2007 Service Pack 1 Update Rollup 4:
–On Exchange 2007 servers that are running Windows Server 2008. Without the update rollup, message waiting indicators will not function properly. See Microsoft KB article 952580.
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/7x/requirements/7xcusysreq.html#wp472166
As a side note but still related, i'm not sure what outlook version you have so make sure it is on the compatibility matrix:
As for the PW (Permission Wizard) it grants permissions for the Unity Service Accounts (Unity Install, Unity Directory Services and Unity Message Store) and to run it you need to be a domain admin. This tool is found on Tools Depot> Administration Tools> Permission Wizard. Make sure it is the latest and greatest version (3.0.0.7) For a more detailed understanding with screenshots go to:
Granting Permissions with Cisco Unity 5.0(1)+ Permissions Wizard
http://www.ciscounitytools.com/Applications/Unity/PermissionsWizard/Unity50/Help/PWHelp_ENU.htm
After you run the PW (Permission Wizard) you will get a pop-up window advising what permissions to apply depending on the Exchange version you choose, in this case:
Version of Exchange in Which Mailboxes Are Homed: Exchange 2007 only
Active Directory Account: Cisco Unity installation and Cisco Unity directory services
Permissions to Grant to previous AD (Active Directory) accounts:
Delegate Exchange Organization Administrator administrative control
Delegate Exchange Organization Administrator admininistrative control
The MSCW (Message Store Configuration Wizard) will define the actual partner. Here is a link with a short description:
https://supportforums.cisco.com/docs/DOC-23513
This tool is found on Control Panel> Add Remove Programs> Cisco Unity Message Store Configuration Wizard> Click on Change/Remove to execute it, below are the screenshots guiding through the tool. **The only screenshot missing is where you see a pencil writting a book, this means it's synchronizing, just let it finish.**
In this case my installation account was unityinstall, however sometimes people name then just Unity, or company_unityinstall and so on so chooose the applicable. For the admin account you could use unityadmi, i decided to use unityinstall:
In the screenshot i only have a 2010 Exchange, however this will reflect all Exchange versions in your deployment (2k3 and 2k7) chooose the applicable, also this will require to stop Unity, so no auto attendant and no voicemail during this time:
On this last part pay attention where it says Directory Service account:
Best Regards,
+|>@|/1D+
