WordPress MU

so I have a server setup with lots of MU blogs like so:

mu.server.com/siteA
mu.server.com/siteB
mu.server.com/siteC
mu.server.com/siteD
etc....

But what I wanna do is:

When someone types in http://www.siteA.com have it show the blog from mu.server.com/siteA but while still keeping http://www.siteA.com in the address bar...

Is this possible? and if so is there an easy way?

It is possible. But you'll need the "Simple Multi-Site plugin and the Advanced Domain Mapping plugin" for your subdirectory structure.

Is there a way to do it that doesn't involve buying something?

Install WPMU in subdomain structure instead and use WordPress MU Domain Mapping Plugin.

but the site is already on a subdomain, will that work?

mu.server.com/siteA
mu.server.com/siteB
mu.server.com/siteC
mu.server.com/siteD

He means the blogs themselves have to be subdomain blogs to work with the free domain mapping plugin.

siteA.server.com for example.

so if i get that paid plugin will it work with the mu.server.com/siteC scheme?

Yep.