How do you play rome total war online?

If you bought the game legally, there should be a "CD Key" printed on a green slip in the box. It is sometimes in the manual too.

Yes, You can. It works fine with windows 7, You just need to change the compability to Windows XP, You can to that by right-clicking on the exe file and click on the compability tab.

Normally not but you can install a app where you can play it without disc.

You use multiple large armies (2 of them should do the job) The huge army that surrounds Rome's strongest unit are Principices(Did I spell it right?) So a medium army consisting of elite troops (i.e....

Yes i can play.