khaan11:
You probably already know this, but there can be no more than 5 culture groups. Therefore, to have a city style that only India gets, you will have to replace an existing city style, most likely the one you want the least.
So, for example, if you chose to replace the asian city style with this southeast asian one, I suggest you do the following things:
1) Make copies of the rASIAN and ASIANWALL files, found in your Civilization III/Art/Cities folder so you do not lose these files.
2) Save the southeast asian cities as: rSEASIAN as rASIAN, and SEASIANWAL as ASIANWALL.
That should be about it. As India already has asigned the asian culture group, if steps 1 and 2 worked, when you go into the game you should see the new city graphics. If something hasn't worked out or I have not made myself clear enough, please say so.
Also, if you plan to replace any other culture group (not the asian one) with new south east asian city graphics, there are a few more steps to installing, and can be a bit complicated. Please tell me if you plan to replace one of the other culture groups, so I can give you more instructions. (That is, if you need them)