You can also try this
Just adding for clarification, because I see some threads where it's still going wrong.
This is the sequence that should be followed;
Uninstall RTW.
Go into Program files/Activision folder, and delete the RTW folder that is left after the uninstall.
Restart the computer.
Now do this...
1) Click Start, then Run.
2) At the prompt type "REGEDIT".
3) Click the "+" next to HKEY_LOCAL_MACHINE.
4) Click the "+" next to SOFTWARE.
5) Select the folder named "The Creative Assembly".
6) If RTW is the only game referenced inside, delete the folder. Otherwise delete all the keys tagged for RTW (inside the creative assembly folder).
Then this....
1) Click the "+" next to HKEY_LOCAL_MACHINE.
2) Click the "+" next to SOFTWARE.
3) Click the “+” next to Classes
4) Click the “+” next to Installer
5) Click the “+” next to Products
6) There should be a list of folders named with long strings of letters and numbers.
7) Search through these folders for a key called “ProductName” that has the value “Rome – Total War™”
8) Delete the folder containing this key.
THEN..... Do a search/find of the registry...enter only the number '1.2' . Press the F3 key to view each reference found containing 1.2. This will take a few minutes to go thru them all, but you should find at least 2 pertaining to the RTW 1.2 patch not previously found.
You will see lots of other 1.2 stuff for drivers and other programs. Ignore these. Do not delete things unrelated to RTW.
After you've gone thru them and found a couple relating to RTW, and deleted them, Restart the computer again.
Now all traces of RTW will be gone from your computer. You can re-install the game, and the 1.2 patch.
Only install the 1.2 patch ONCE. Trying it twice cause problems and you may have to do this all over again.
This worked perfect for me today, after struggling all day long trying to get the patch to reinstall without searching for the 1.2 in the registry.
Also, some of you in the other threads are not fully deleting the game before doing the registry, or trying to re-install. Do it exactly in the order I have listed here, including the two restarts, and it should work for you.