Driverguide.com and eMachines only has drivers for Vista (the OS that came pre-installed in the T3642).
Realtek Audio/Sound Driver for eMachines T3642
Description: Audio Driver
File name: Audio_Realtek_126.96.36.19985_Vistax86_A.zip
Size: 17.5 MB
The only way I can possibly find a Windows XP driver is if you can give me the hardware id for the device. In Device Manager, double-click the device, click the Details tab, give me the 1st line of text. Should start with PCI\VEN........ Copy it carefully as just 1 error will make it impossible to help. And a description of the sound chip would be helpful as well as we don't know what Realtek audio chip eMachines used in this machine.
Or.... you can try some of the Realtek HD audio drivers posted in the REALTEK STICKY
near the top of this forum.