Very slow loading of CHM files

If I double-click on a CHM file (any one, even the ones in the Windows
\Help folder), the help program comes up, the correct title displays
in the title bar, but the main window stays blank with the mouse
pointer set to the hourglass for several MINUTES before the file
finally displays. There is no significant disk utilization during
the wait, and the CPU utilization of the hh.exe process is at zero.
"Help and Support" seems to work fine.

I tried uninstalling KB925902, but that didn't help. I tried copying
hh.exe, hhctrl.ocx, itss.dll, and itircl.dll from another system, but
that didn't help. I downloaded Mjsdiag and had it reregister all the
help DLLs, and that didn't help. Any ideas? Here's the relevant
parts of the report from Mjsdiag:

Operating System: Windows NT 5.1.2600
SysLocale.DefaultLCID: 0x0409 (1033)
SysLocale.PriLangID: 0x0009 (9)
SysLocale.SubLangID: 0x0001 (1)
DecimalSeparator: .

HH Installed: YES
HH Version: 5.2.3790.2847
HH Friendly Version: > 1.4a

H2 Installed: NO
H2 Version:

IE Installed: YES
IE Version: 6.0.2900.3059
IE Friendly Version: Internet Explorer 6 (Windows XP SP2)

File Registered OK: C:\WINDOWS\system32\hhctrl.ocx (Version:
5.2.3790.2847)
File Registered OK: C:\WINDOWS\system32\itss.dll (Version:
5.2.3790.2453)
File Registered OK: C:\WINDOWS\system32\itircl.dll (Version:
5.2.3790.2453)

File Found: C:\WINDOWS\system32\hhctrl.ocx
Version = 5.2.3790.2847
Registry Info: {adb880a6-d8ff-11cf-9377-00aa003b7a11}
ClassName = HHCtrl Object
InProcServer32 = C:\WINDOWS\system32\hhctrl.ocx
ProgID = Internet.HHCtrl.1
DLL is Found and Registered OK = YES

File Found: C:\WINDOWS\system32\itss.dll
Version = 5.2.3790.2453
Registry Info: {5D02926A-212E-11D0-9DF9-00A0C922E6EC}
ClassName = Microsoft InfoTech IStorage System
InProcServer32 = C:\WINDOWS\system32\itss.dll
ProgID = MSITFS1.0
DLL is Found and Registered OK = YES

File Found: C:\WINDOWS\system32\itircl.dll
Version = 5.2.3790.2453
Registry Info: {4662DAA5-D393-11D0-9A56-00C04FB68BF7}
ClassName =
InProcServer32 = C:\WINDOWS\system32\itircl.dll
ProgID = ITIR.WordWheelBuild.4
DLL is Found and Registered OK = YES