The wallets are located at different locations on your computer.
For Electrum, the wallet is located here:
C:\Users\YourUserName\AppData\Local\Electrum
For Bitcoin-Qt, the wallet is located here:
C:\Users\YourUserName\Appdata\Roaming\Bitcoin
So you can run both clients on your computer at the same time without problems.
Each
client (e.g. Electrum) creates their own wallet and each wallet has their own address. You can send money between the wallets by sending the money to an address in the other wallet. You can also import the wallet from one client into another to combine the wallets.
If you want to, you can import the wallet from Electrum into Bitcoin-Qt, just see
this link.
You can do the same with any other client. If you want to move the wallet to another client, you need to "export" or "dump" the
private key which is what you want to import into another client. Every wallet should have a "import wallet" or "import private key" function, just look at their help or wiki page.