Just as a follow-up. NAC no longer appears to be including the pc_XP32 check as part of an active rule. Based on dredging our logs, there appears to be no comparable failures on Wow6432node on 32-bit machines after NAC's midnight auto-administration on 11/15/2008. Similarly, pc_XP32 no longer appears as a Passed, Failed or Not Executed check for post-XPSP3 updates.
Thanks. Terry
