On reading the initial post, I also thought what Jon thought, that she wants to create a music performance to post at a website--this doesn't even need to be midi sequencing anymore--USB and firewire devices like MBox (and a number of others) allow you to plug your guitar, keyboard, and/or a microphone directly into your computer--you can record directly, input MIDI into a sequencing program, or do both into the same file. I've seen devices that convert analog to digital and also manage midi input for as little as $150(MBox is about $400)--software included.

These things input into a laptop, which is great, and many, if not most are both Mac and PC compatible--so the good news is that the inexpensive laptop recording studio is finally here--the bad news is, the more stuff there is to do, the steeper the learning curve--