You run into issues installing Exchange 2007 SP2 on SBS 2008 until you add the following key and DWORD to the registry.

To create the E12SP2READY registry value, follow these steps:

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\Software\Microsoft\SmallBusinessServer\Exchange

   Note If the Exchange subkey does not exist, you must create it. To do this, follow these steps:

   1. Right-click SmallBusinessServer, point to New on the Edit menu, and then click Key.
   2. Type Exchange and then press ENTER.
3. After you select the Exchange subkey that is specified in step 2, point to New on the Edit menu, and then click DWORD Value.
4. Type E12SP2READY, and then press ENTER.
5. Right-click E12SP2READY, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. On the File menu, click Exit to exit Registry Editor.

Full article at Microsoft - http://support.microsoft.com/kb/973862

There are additional steps to get Exchange 2007 SP2 installed on SBS 2008, below are the steps to complete from Microsoft Support

http://support.microsoft.com/default.aspx?scid=kb;EN-US;973862

How to update the GAL manually

Update-GlobalAddressList -Identity <GlobalAddressListIdParameter> -DomainController

For most it would be Update-GlobalAddressList -Identity “Default Global Address List”

How to check the logging in Exchange 2007

get-EventLogLevel

See which certificates Exchange 2007 are using

Get-ExchangeCertificate

Get-ExchangeCertificate |fl  (for more information)

Enable Exchange services for certificate

Enable-exchangecertificate -services IMAP, POP, UM, IIS, SMTP -Thumbprint BCF9F2C3D245E2588AB5895C37D8D914503D162E9

See what URL the CAS server has for autodiscover

Get-ClientAccessServer -Identity CASServer | FL

Change the autodiscover URL

Set-ClientAccessServer -Identity CASServer -AutoDiscoverServiceInternalUri https://mail.yourdomain.com/Autodiscover/Autodiscover.xml

Configure all the InternalURLs for each web distributed service

Set-OABVirtualDirectory -Identity “CASServer\OAB (Default Web Site)” -InternalURL https://mail.yourdomain.com/OAB

Enable-OutlookAnywhere -Server CASServer -ExternalHostname “mail.yourdomain.com” -ClientAuthenticationMethod “Basic”-SSLOffloading:$False

Set-ActiveSyncVirtualDirectory -Identity “CASServer\Microsoft-Server-ActiveSync (Default Web Site)” -ExternalURL https://mail.yourserver.com/Microsoft-Server-Activesync

Find out your inbound/outbound message limits

get-transportconfig