I recently digged into this, and this might be the answer: the only hotfix included in the MSURP1 which requires an updated HALMACPI.DLL is the KB835730 fix. The KB article also mentions P4 HT and "the C3 power-saving state", so I borrowed a P4 laptop with HT and tried all post-sp4 versions of HALMACPI.DLL. Version 5.0.2195.6988 mentioned in the KB artivle and all later versions seemed to have this problem. Second time I tested I modified the registry after installing the KB835730 fix as described in the KB. That certainly made a difference with all versions of this file - even with the MSURP1.
The registry change I'm referring to is this
• Edit the registry Add a DWORD value named 14140000FFFFFFFF that has a value of 00000010 to the following registry setting: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\HAL
Maybe MS forgot this setting in the URP1 (it's not there - I checked) ? Or maybe it only works with Dell hardware? Dono