Absolute Newbie Midi Qestions... Options

[postalblowfish7]

Ok, I just got the Edirol UM-1 USB MIDI Interface and connected my Yamaha DGX-500 to my Dual 1.25 Ghz G4 Powermac. I set up MIDI in Digital Performer 4, and sequenced a little song. I have it set up with the Apple built in piano intrument and I was wondering how I can get different MIDI intruments installed into DP4. I also have no idea where I can get these instruments. Are there packs of softwear instruments I can buy? Also, I really like the patches on my DGX-500 and would love it if I could get softwear instruments from Yamaha of the same patches. As you can tell i know absolutely nothing about this brave new world and I would apreciate any help I could get .