Cant you just click add folder and then add the CD drive and then do it agin for the other drive? if not im pretty sure if you put like
D:\Music\[all you mp3's here]
E:\Music\[More mp3's]
then just click add dir and just add both music folders off both drives i am pretty sure it would work i dont got any disks with mp3's around so i cant test but should do
Edit: then you woudl do the same and add the folder with the music on your hd and then just tell winamp to play random tracks