First, before we move on, make sure that you have windows up to date and all the latest drivers for your device.
OK, for starters, if you have windows vista try this:
In windows vista, the "stereo mix" is disabled by default. It being a virtual sound card, most people have trouble finding how to to enable it seeing as it does not show up in device manager. To enable the virtual sound card in Windows Vista, open the control panel, then sound: Control Panel-->Sound-->Recording Tab. Now right click the window. You should have two option appear that says "display disabled devices" and "display disconnected devices". Make sure "display disabled devices" is selected. A sound card called "stereo mix" should appear. Open the device properties and enable. You should then have your stereo mix in the audio control. Should should then be able to select that sound card from the list in your recording software's settings. (You may have to restart your computer first.)
If you are using a version of windows other than vista, or if you are using a laptop and want to record a stereo mix without playing audio through your speakers there is a great program out the called "Virtual Audio Cable" (VAC). It installs what a virtual sound card on your pc, well sort of... it allows you to set up a virtual patch bay system with multiple audio feeds. You could set the VAC output device as your primary sound card, then record from it. I will include a better description as well a a link to this software. The only downside is it cost $30 USD, but in my opinion, this someware is worth the price if you are doing a lot of recording.
A third alternative to buying software would be VLC media player. VLC media player has the option of saving any open streams to almost any file type. It opens streams from web streams, local files, as well as audio and video devices. It can also be conersed into converting files very nicely although this may take some practice will file formats, etc. It's free. I will include a link.
-Chris-
PS: Here's that VAC description I promised.
VAC is intended to connect several audio applications together in real time. It's like a sound card with hardwired input and output: when an application sends an audio stream to a virtual cable, other applications can record this stream from the other cable end. Thus, you can record and process output of almost any audio application by almost any other audio application.
Windows Vista bundles drivers for the Realtek 8169 chipset, so you are unlikely to need to download them. They are available on Realtek's support site (in the Related links section below).
Realtek was created in 1987.
Realtek's population is 1,600.
what does realtek audio do
RealTek Audio Druver
Use windows update, it will automatically locate missing drivers (sometimes it does not work).
You should check the realtek website. All required drivers should be available there for your laptop audio device as well as any other realtek audio devices you may be using.
Try the Realtek site at www {dot} realtek {dot} com {slash} download.
Do you actually have a PnP Realtek soundcard? (An added-on, plugged in physical card you have installed into your computer frame) Or are you trying to find the sound card driver? (This seems more logical) If this is the case, there are a variety of Realtek sound devices. You can go to this site, and if all you really need is the driver for your sound card, you will be able to download it free .http://ptf.com/realtek/realtek+sound+card/
You can buy realtek drivers online at the following sites I found for you to have a look at. Here are the sites I found www.realtek.com.tw/downloads , or www.realtek.com.tw/
RealTek's latest version is 2.63, but you should make sure that your motherboard manufacturer has not done some customizing to the Realtek hardware. The best place to get the latest version for your computer is the computer or motherboard manufacturer's website.
A generic driver for the RealTek RTL8139D can be found at the link below. Note that Windows 2000 and later should already include this driver by default. You can also visit Getdriversnow website and download free driver for Realtek ethernet driver. Just follow the link below.