it depends.
if you buy a flash template that you fill out with you information or someone does for you, and you have it sitting as a bunch of files. then its a simple thing to do.
if the template starts to include server side coding/ databases and what not (which it probably doesnt) then you run into a challenge.
if you get a folder full of files that works in any location, then all you will have to do is upload it to the ftp, find the http link that goes to the homepage, and direct your domain to that.
Give it a try, and if you need any help im sure you can find it for little or no cost in good time.