ic..what if i have multiple wallet.dat? how can i set them to the client so it recognizes that there diferent
If you are swapping different wallets, you simply close the client, back up the current one, then replace it with the other one.
Or some people keep multiple wallet.dats on a drive at the same time (e.g., each gets a different name) and use a symlink to point to the one they want to use.
Other clients support multiple wallets. Multibit, I believe, is one of them.