Can't speak to MC because I've never used it but it sounds like you could REALLY use an external drive to clear up your system drive. If your current system is working (the specs are moderate but fine) then I wouldn't get too wrapped up in building a new machine unless you really want to.
Even a spindle of writeable DVDs to archive old work would be good. If it's a ton of sample banks though that you want access to consider installing a second drive on the system (if it's a tower... if it's a laptop then again a fast external drive could help).
Make a system image (stored to a safe location off system like an external drive or series of DVDs) too if you haven't already so if any of the components on the system goes boobies up you can get it all back.
If MC7 is as drastically different from MC5 as Gregy says then you may want to consider just snagging Sonar (Artist is pretty inexpensive but of course Pro and Platinum are WAY better with more creative tools). My reasoning being that if you are going to have to go through a major learning curve you might as well make it count. You'll find it's much easier to get help with Sonar than Music Creator because that's what most of us around here use and Sonar is in constant development with new goodies coming every month.
Just some thoughts.
Now some OT action...
Karyn
Welcome to the forum William,
You'll be able to add links when you've made a few more posts.
Ain't seen you in a while, Karyn. Was wondering about you a little while back. Hope all is happy and well.
Cheeeeers!!!