There do however seem to be plans to enable iAMT functionality in SCCM 2007, some details (no dates unfortunately) can be found in this document: SMS Solutions Brief
I don't think the current addon will run with SCCM 2007 at all, whether you install it before the upgrade or afterwards.
To expand on Alex's post...
The SMS 2003 Intel AMT Add-on is not supported on SCCM; however, Intel will continue to provide support for Intel AMT Add-on on SMS 2003 in alignment with Microsoft's SMS 2003 product lifecycle.
Microsoft will provide native support for vPro AMT v3 features and provisioning in SCCM 2007 with the implementation of SCCM SP1 expected Q2 2008. To provide backward compatibility for vPro and Centrino Pro AMT v2.x clients, Intel will provide a SCCM WS-Translator which is expected to release around the same time as SCCM SP1. Other then the WS-Translator, Intel currently has no plans to provide an Add-On for SCCM.
For Microsoft TAP customers, the System Center Configuration Manager 2007 Service Pack (SP) 1 with the native Intel vPro technology support is now available on Microsoft Connect. Go here for the full announcement:
Please note that SCCM SP1 does not provide native support (yet) for vPro Clients that are based on firmware versions 2.x (both desktop and laptop) due to SCCM SP1's use of the WS-MAN protocols for manageability and AMT 2.x exclusive support for EOI. Intel is in the process of developing the WS-MAN translator that will provide backward compatibility for AMT 2.1, 2.2, 2.5, and 2.6 vPro Clients. WS-MAN release is tracking for an on-time availability with Microsoft RTM release of SCCM SP1.