I meant to reply to this thread... sorry guys...
Check out Diablo Sampler. It allows you to play different samples in random order when ever you want them to. You can have a sample every 60 seconds 900 for every 15 minutes. It has additional mixing controls to blend the sample with your source just perfectly.
You can also record samples with this too. Lots neat little features like pitch change, loop and delay as well as a reverse sample feature.
You will need a stacker program to use this with the shoutcast source plugin(both use DSP/Effect) in winamp.
My current configuration is
sqrsoft crossfading (output with Shoutcast Dsp)
muchfx2(DSP/Effect with diablosampler,octimax)
I like and am currently using it. You can get it here: