There are a number of ways to do this. You can copy the button layers and paste them to the other PSD.
- Ctrl+Left Click on the layer picture to select the layer.
- Ctrl+C to copy
- Right Click the layer discription and select "Copy Layer Style"
- Ctrl+V to paste on the other PSD
- Right Click the layer discription and select "Paste Layer Style"
If that doesn't work out for you I can think of some other ways.