I'm assuming that by "bank", you mean you've transferred the Bitcoins out of Mt. Gox back to yourself.
If that's the case, and you want to add Bitcoins to Mt. Gox, start by logging into mtgox.com. Go to the "Add Funds" page and scroll down a little to the "Add Bitcoins" section. Type in the number of coins you want to add for this single transaction and click "Send Bitcoins".
Mt. Gox will give you an address. Copy it. You'll use it once (and only once).
Go to your Bitcoin client that has the coins in it, and click "Send Coins". Paste in the address you just copied, and type in the same amount you entered on the Mt. Gox site. Now just wait a bit, and the coins will show up in your Mt. Gox account.
Thanks I was wondering that too. I set my account up but hadn't gone that far...