I have a creative SoundBlaster LIVE! 24 Bit External Sound Card and this annoyed me for weeks.
depending on your surround sound reciever depends on the solution.
i have an Acoustic Solutions surround sound system with coxial and optical inputs, aswell as stereo red & white jack inputs.
not knowing the method or connection your using makes it difficult to give you a single solution so i'll list a few.
The soundblaster software shoudl include the Creative Audio console with all sorts of effects, one is CMSS (CMSS-3D) Stereo widening which is still stereo but gives a surround sound effect.. but i'm guessing you payed for 5.1 and you want 5.1 onto the next part
5.1 surround sound can only be produced when the actuall audio your playing contains 5 channels of audio, for example you cant play a stereo song in 5.1 surround sound without some sort of hardware or software sound manipulation. Luckily my surround sound system has Pro Logic II built in and some other effects which convert a 2.1 signal to a 5.1 signal and it works brilliantly. I'm not sure of a software alternative.
setup for your soundcard will be different under XP and Vista also, but there should be a properties option for your sound device where you can select your speaker setup such as headphones, built in speakers, 2.1 speakers, 5.1 speakers, 7.1 speakers and you should be able to manage this from the creative software.
If using Coxial / Optical or SPDIF under vista you MUST set the playback device as SPDIF, at least you have to with my sound card and drivers and seems to be a limitation of the actual sound card drivers for vista.
Personally i was looking forward to hearing the windows login melody in 5.1 surround sound too, but this doesnt happen.
Infact i find that almost all programs bar a few will not play Dolby Digital or DTS 5.1 surround sound via any or my output options hence the next solution..
if you have the 5.1 sound but winamp simply just plays it in stereo try the following.
You need to use DirectSound Output:
Preferences (Ctrl-P) > Plug-ins > Output > Select "DirectSound Output"
That should work in most cases, but if not, then:
Checkmark: "Allow hardware acceleration" in DirectSound Output config,
and make sure your sound card/chip is selected as Output Device.
Note that any changes will take effect only after playback is restarted.
In some cases, a Winamp restart is required.
If that doesn't work make sure you have the latest version of DirectX
(v8.x or higher is required)Winamp 5.25/5.3 and higher
For actual multi-channel files (ie. aac/wav/ac3/ogg/wma files encoded in 5.1ch surround, as opposed to standard 2-channel stereo mp3's), you need to checkmark "Allow surround sound" in 'Winamp > Prefs > Playback' for the music to play in its original 5.1 channel format (Note that this setting is checkmarked by default).Windows Vista
In addition to the above instructions, Vista users will also need to go to:
Control Panel > Sound > Playback tab > Speakers > Configure:
Select: 5.1/7.1 Surround.
Control Panel > Sound > Playback tab > Speakers > Properties > Enhancements tab
and checkmark "Speaker Fill"
Hope this helps