CUBASE problem

[Guest snowball]

I have a Delta 10/10 working on a MAC OSX Dual G4 with 512 MB Ram But every time I run Cubase SX I get this Message: "Couldn´t get Sample Rate. This may be due to Midiclock set on EXTERNAL". But I checked it and I was set on INTERNAL...I also have problems with the VST performance. With only 3 MIDI chanels with 3 inserts such as reverb, Dynamics and Double delay, and one audio track, I GET 50% full on my memory perfomance!!!! this shouldn´t be happening because of my RAM amount but it does!!! I recently changed from PC to MAC so I really don´t know how to fix this...PLEASE HELP!!!