On Windows 2003 user regedit.
On Windows 2000 user regedt32.
First make a backup of your registry.
Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\C896E102E88BEA14C864B3ABACCD6D7E\Patches
On the left hand pane, below this \Patches key will be a variety of reg keys that represent the GUIDs of BE hotfxes and service packs that have been installed, delete each of these keys.
On the right hand pane there is a key called AllPatches.
Open this key (again for Windows 2003 regedit is fine, but for Windows 2000 you must use regedt32) and empty out its contents; you should be able to just hit the Backspace key on the keyboard.
You are done with this key.
Now browse to HKEY_CLASSES_ROOT\Installer\Products\C896E102E88BEA14C864B3ABACCD6D7E\Patches
On the right hand pane there will be some keys that display the GUIDs of the BE hotfixes and service packs that have been installed.
Also on the right hand pane is an additional \Patches reg key of type REG_MULTI_SZ.
Delete the keys on the right hand pane that display the GUIDs.
Still on the right hand pane, Open the (REG_MULTI_SZ) \Patches key (again for Windows 2003 regedit is fine, but for Windows 2000 you must use regedt32) and empty out its contents; you should be able to just hit the Backspace key on the keyboard.
Below are some examples of the BE hotifx and service pack GUIDs
SP2 66491A51A43069648AA275E5A4E2BDD9
SP3 7E69932F48D43D84890E6B292C9E1094
HF47 E5866158DB0276041A35233CED489727
HF50 EAABEB068F14465459B63C8D5DAD9B2A
HF51 35C60F7F92418ED42B25287D3A5683E9
HF52 1A42F459EA25FED41BA5823BA2CA67F6
HF54 63E588DEC470F354EB8D3BCC32E877F5