My studio setup includes an imac G3 400 w/ MOTU 828 and Midisport 2x2 and Cubase 5.0r2.

1.I can record analog audio through the MOTU 828 using cubase w/ no problem.

2.My midi and OMS setups are okay and cubase is receiving a midi input signal from my keyboard.

The problem is, I can't get the VST instruments to play back through the computer. At some point in the past I was able to get this to work. I have tried everything I can think of but there seems to be a problem w/ the output of cubase or the computer's sound output. Any ideas would be appreciated.

Please forgive my newbie ignorance.

Is the rest of your audio playing back ok out of the outputs?
if so then the problem really does lie with cubase/vsti's
remember that the vsti's have effectively 2 tracks, one for audio ,and one for the midi.
you need to make sure the audio vsti channels you are using are routed correctly to the master output, and faders up as well as the inputs selectd appropriately.
Forgive me if i go too basic, just trying to be helpful from the ground up.
When you record the midi track for that instrument you are recording to a midi track , which is passing it thru to the vsti.
the audio from the vsti will appear at an audio track dedicated to its audio, generally i find people forget to set up these audio object tracks correctly.
check your manual regarding this, as i cant recall all the little details without going and running mine up, as i'm not in the studio at present but in the living room.
If youre still stuck, give us a yell, max.hodges@ntlworld.com, and i'll run thru the process step by step when i've refreshed myself on exactly which bits you need for V5r2, as i mostly use logic these days.
best regards
max