By default Windows installed High definition Audio drivers for this this model in Windows 7. In case there are no sound coming up from your eMachine 525, you need to update the BIOS.
1. Download this BIOS update:
BIOS_eMachines_3.04_A_A.zip (direct from Acer)
2. Extract, and run the exe file to flash the BIOS.
3. Restart and your sound should work now.