Firefox install fail - access denied error -202

Hi,
Have downloaded Firefox 1.0, also have the install exe on disc, but when I 
run it the Browser installation fails with Error -202, Access Denied. The 
wizard.log shows failure occurs in different places each time, for example:-

     ** folder to delete: C:\Program Files\Mozilla 
Firefox\defaults\profile\US\
     ** File to delete: C:\Program Files\Mozilla 
Firefox\defaults\pref\bug259708.js\
    ** ERROR (-202): Replacing: C:\Program Files\Mozilla 
Firefox\chrome\browser.jar
     ** addDirectory() of Program returned: -202

     Install **FAILED** with error -202  --  2005-02-21 18:50:36

I'm rebuilding my system after a hard disc crash, and starting affresh with
XP Home + SP2. The only difference between my old XP Home system where it 
installed no
problem, and this new one, is it now has SP2 incorporated.
Microsoft Firewall is OFF, I'm running the latest free Zone Alarm 
(5.5.62.4).
Also running the Beta version of Microsoft Anti-spyware.  I've tried turning 
off the
checks in the latter but this makes no difference.
I am logged in with Administrator status.
I can't uninstall Firefox because it didn't get far enough to "register 
itself" and there is no uninstall exe.

Have shut down all internet activity, and disabled the Microsoft 
anti-spyware, deleted everything in the %TEMP% folder, deleted the Mozilla 
Firefox folder, and retried the install, still error -202!

It's my Birthday today, and  a working Firefox would be a nice present - any 
helpful suggestions would be very welcome,
Thanks,

Tom