how to transfer a app from one ipod to an iphone?

• Connect the device with the app to the PC with a USB cable.
• Right click on the iPod and select "transfer purchases"
• Once the app is on the computer, then connect the iPhone.
• Set up that app to sync and you should be done.

Yes it is certainly possible. You need to sync your iPod via iTunes on your PC. All purchased apps should then appear in iTunes. You can then transfer them from iTunes to your iPhone.

Additionally, I recommend syncing with a computer regularly to ensure you have a backup of all your data. You are backing up right?

Here is Apple's support documentation on syncing: http://support.apple.com/kb/ht1386