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So what you are suggestiong is just using Cubase as the recording software?Log on to the Edirol, M-audio and Terratec websites and have a look at what they have to offer. I will say this make sure you have a fast processor and at least 1 Gb of ram, an external hard drive for archiving your stuff would be handy and a decent VST program like Cubase 5. Pro tools canj generate M.I.D.I. but it does not support VST's as far as I am aware (At least the version I've been using doesn't the new HD version might?) so a decent VST will start you off in the right direction plus you can record audio in Cubase 5.
When it comes to buying your gear take time you will be using it for a long time.
Good Luck