ZumoCast is a great app but I felt it fell short on it's ability to stream music. Huge gaps in the stream made it nearly impossible to listen to music unless I was right on top of my router.
Stream to Me works a bit differently. It doesn't give you the access to your computer that ZumoCast does but it does a better job of streaming music. Maybe video too, I don't know I haven't tried that.
I think the difference in quality of streaming stems from the fact that with Stream to Me you have to install an app called Serve to Me (free) on your Mac or PC. I was doing some work around the house yesterday with my Motorola S10 headsets on going from room to room and the stream had very little break up.
Also ZumoCast only located 1000 of my songs. Stream to Me located all but 4 songs on my list of 10 days worth of music.
You probably would want both because ZumoCast can be valuable for downloading documents and Stream to me doesn't do that but it's definitely something worth investing a few dollars in.