I have a wk3000, connected to my pc. I have Voyetra record producer and Power Tracks software to record midi songs. When I use record producer(been using this one so far), I record one track(drums), then go on to record another(bass). When I playback, it plays in the last sound I have the keyboard set to(all tracks play drum sounds, bass sounds, piano sounds, etc). How can i record tracks and they STAY playing what I've recorded them in?

Tracks are like 'boxes' that you fill with information. Channels are the 'content', that you put in the 'box'. You must 'define' the instrument that you assign to a 'channel'. With out assigning an instrument....the track will default to the current selected instrument (what is happening to you). The track doesn't know what instrument to use...if you don't tell it...by making a channel selection (1 to 16), then making an instrument selection for the channel.
In Power Tracks (I have ver.10)...you make the channel assignments in the 'track' display...by left clicking on the '5pin' icon...that is on the left side of the 'track' display. Then click on the 'channel' and assign 1 thru 16...to the track. Next, click on the word 'program'...and select an instrument from the list.
Voyetra record...should have a similar type setup for recording midi.
Remember...a track needs to have a channel assigned to it, and the channel needs an instrument assignment.