I do not know the card, so this is just a suggestion.

So now you have to shut down Cubase to play winamp or do you have to disconnect your soundcard?

Your soundcard should have the possibility to activate WDM output on any of its physical outputs. Then in the audiosettings of XP (I assume you run a Windows machine) your audio settings should appoint the Lambda card for audio playback.

I run Cubase through mLAN. I can switch back and forth playing with Cubase, WMP, Audition, Moviemaker even, through the WDM output that I can enable in the graphic patchbay. The only drawback is that those channels are then sacrificed for simple stereo playback and not available for anything else.

You may also need to check the "release asio driver when in background" box in the devices set-up menu?

When I try to play a song in Winamp while Cubase is running, I get this alert: "Bad DirectSound driver. Please install proper friveres or selevt another device in configuration"
All drivers are installed (as far as I know) and when I look in the control panel, everything seems to be allright.

I tried to check "release asio driver when in background" check-box, and
Cubase works until I start to play a song in Winamp, then I stop it, and when I try to play something in Cubase again, I just don't get any sound.

thnx for your help this far =)

You need to make sure that Winamp releases the driver when it is in the background also, so that Cubase can go back to using it. I don't know how to do this though because I don't use Winamp. I would imagine it's about the same procedure as doing it in Cubase.

get a 10$ soundcard (or use the built-in one if your PC has it) and connect the OUTs to whatever playback system you are using for listening to WINAMP.

Swtiching drivers back and forth bewteen two programs during a session is not what I would describe as a fun thing to do :)

yoooooooooo hoooooooooooo !!!!!!!!!!!!!!! the wombat gave ya the answer... ya have to release the drivers in the background....