Multiple wallets on BT client but only one wallet file

[deltree]

Hey guys, this is very noobish but I happen to have created 3 different wallets on one client. The backup dat file generated I believe contains all three. What If I wanted to move one of the addresses out to another pc and have only two wallets remaining on this pc.

What's the solution for this kind of a problem? I thought there would be seperate wallet files for each if the addresses are different.

Am using the official bitcoin client for windows btw!