The "Unlock Only" patched SYSSETUP.DLL will skip the signing verification of the SYSSETUP.INF file responsible for components installation, and make it possible to customize Windows installation with some modifications to this INF.
The "Unlock & OOBE", naturally, does BOTH.
PE Checksums are included in the second commented line of the INI for each addon. If MS releases any more updates to Syssetup.dll and they are ever inlcuded in an RVMUpdatePack, you can use that (and future) checksums to modify the RVMUpPck.inf.
Hacked syssetup.dll
Okay. We now have 6 SYSSETUP.DLL files to play with, as follows:
(note: The downloads with _HF_ are the ones Build 2659)
LINK - OOBE Only: Zacam_Hacked_SYSSETUP_Addon_OOBE.cab
MD5: E7353996F2F45C9F590802F43F24D914
SIZE: 321 KB
LINK - Unlock Only: FoxyZacam_Hacked_SYSSETUP_Addon_VerSkip.cab
MD5: 068ED358A76E72409A7012F1A0D07FBD
SIZE: 321 KB
LINK - Unlock & OOBE: FoxyZacam_Hacked_SYSSETUP_Addon_OOBE_VerSkip.cab
MD5: A7D71949A8458FD34EA1398B3AF90EE6
SIZE: 322 KB
LINK - OOBE Only: Zacam_Hacked_SYSSETUP_HF_Addon_OOBE.cabLanguage: English Only!
Dll Version: 5.1.2600.2180
Release Date: 2004-08-04
Op System: XP Only!
MD5: 7C1B3F70D556772E93776B422A0D999F
SIZE: 320 KB
LINK - Unlock Only: FoxyZacam_Hacked_SYSSETUP_HF_Addon_VerSkip.cab
MD5: 24B164D3A94641DBB59B8D030F77380C
SIZE: 320 KB
LINK - Unlock & OOBE: FoxyZacam_Hacked_SYSSETUP_HF_Addon_OOBE_VerSkip.cab
MD5: DCBC97075B389C4C39E70CE587D0A647
SIZE: 320 KB
Credits:Language: English Only!
Dll Version: 5.1.2600.2659
Release Date: 2005-04-21
Op System: XP Only!
For patched file to skip the signing verification, Philippe. Homepage Azimut Project. Released with permission.
OOBE patching done via information found at this MSFN topic, all credits to Gosh, ZoSTeR and Zacam (for patching).
And to Aserone for releasing the first patched syssetup that started this whole cascade of updated files, and for being really cool about me (zacam) updating it.

Edit 2006-05-12 - I or Zacam will try to patch the newest official build 5.1.2600.2659 (call hotfix).
Edit 2006-05-12 - Updated to include combined hacked syssetup.dll by Zacam
Edit 2006-05-12 - Zacam went psychotic and decided that 2 of one version and 1 of another wasn't good enough and balanced it all out by making 3 for each and then asked RyanVM _really_ nicely to host them.
Edit: 2006-05-13 - Zacam rewrote the original release (thank you man!), moved up to topic