If you have the new market, you can use two gmail accounts and download the apps from your old account. Push your menu button, then go to Settings > Accounts and add your old Gmail account. Then load up the new market (it's the one that tries to sell you books and movies) and push the menu button. Then go to Accounts. Select your old gmail account. Then hit menu again and hit my apps. If you don't want any of the email from your old account, just make sure it doesn't autosync anything in the account section. I use 2 gmail accounts with my market and it works flawlessly.