Okay, steps given below. Its not nearly as difficult as the number of steps below seem to suggest (carrying out all of the below will only take 5 minutes in total). If you don't want to make another post saying "doesn't work" following the below EXACTLY will help, lol. Here we go:
Maxthon as default browser on Windows XP (SP1 or higher):1. If you want to disable IEAccess, then have the necessary values for that in winnt.sif, otherwise go to next step.
2. Ensure that OEMPreinstall=yes in winnt.sif.
3. Since Maxthon is based off IE and will use its settings too, look-up this topic for IE configuration -
IE6 pre-config.
4. Install Maxthon manually.
5. Configure it to how you like it (the settings, toolbars, etc.)
6. Just before you close it, set it to ask "Do you want to make Maxthon your default Browser" (from "Options >> Startup" menu) - Since that is what will set the protocols to Maxthon after asking you, upon first-run.
7. Copy away Maxthon's installed folder (C:\Program Files\Maxthon) to elsewhere to have a safe copy.
8. Now put that folder onto your unattended CD - "\$OEM$\$Progs\Maxthon\" folder should now exist.
9. Explanation - The above way, during windows setup, you have it being copied automatically to "%ProgramFiles%\Maxthon"
10. Put the short-cut to Maxthon too - make a shortcut to it on the desktop, and put it as - "\$OEM$\$Docs\Default User\Start Menu\Programs\Maxthon.lnk"
11. Now, the registry entries in next steps. Put these in any of your existing .REG files, which are applied at T-12 (through cmdlines.txt).
12. Of course, remember that since its more complex to make registry entries path-independant, all the paths below are absolute paths (its more difficult to use system variables like %ProgramFiles% in .REG files). So change the paths according to your installed folders.
13. Self-explanatory registry entry
CODE
; remember Maxthon setup folder
[HKEY_CURRENT_USER\Software\Maxthon]
"Folder"="C:\\Program Files\\Maxthon"
14. Self-explanatory again:
CODE
;Make Maxthon the default browser from Start Menu
;Set the Start Menu sticky apps
[HKEY_CURRENT_USER\Software\Clients\StartMenuInternet]
@="Maxthon"
; Give details for the Internet Browser (as mentioned above)
[HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\Maxthon]
"LocalizedString"="Maxthon Web Browser"
[HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\Maxthon\shell\open\command]
@="C:\\Program Files\\Maxthon\\Maxthon.exe"
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\Maxthon]
@="C:\\Program Files\\Maxthon\\Maxthon.exe"
"Path"="C:\\Program Files\\Maxthon"
15. That's all. Make your CD and it should work. No IE, only Maxthon.

Enjoy!
Note that after your first install of Maxthon once, there's no need anymore to use the original installer in which it came.
If there's any errors in the above (well, other than the bad points relating to absolute paths), do post and tell. Hoping this helps....