I had the same problem after installing Windows XP SP2.
After hunting through the Microsoft KB I found the
following link which provided all the details I needed to
solve the problem:
http://support.microsoft.com/default.aspx?scid=kb;en-
us;281679
(copy and paste above if you cannot click it)
I only had to regsvr32 all the dll files in order to
solve my problem, but your mileage may vary. You should
also try setting up the dcomcnfg default security
settings if you have 2000 or later Windows (on the
default security tab in Windows 2000, in WinXP it's a
little different where you have to open the top item in
the tree, open the top item you expand to, then
repeat 'till you see My computer and right click that
then choose properties and choose the security tab). Then
click both edit defaults buttons, making sure SYSTEM and
INTERACTIVE are both listed in each one. Add them if
needed and check all the allow items for them. Repeat for
the other edit defaults button, OK everything, exit
dcomcnfg and log off and back on. (Didn't get that? It's
in the KB, too.)