ManM ... you need to install the VST according to it's installation directions.
remember where it was installed or where you opted to have it install. (the directory location)
then open MC and navigate to the PLUG IN MANAGER. you will need to use this to ADD the new plug in to the scan list. Then let it run the scan again.
Now, when you choose a synth, you should see it in the list. Note.... that it may not end up in it's own folder on the list of available synths if you're not paying attention to where you choose to ADD it. for example in my Sonar synth list, somehow, a few of my synths are in a group with others.
I thought the install had failed until I clicked a few of the groups (indicated by a black right pointing arrow head.....and there it was..... it runs fine from there, but it certainly threw me off for a bit until I found it.