Is there a free virtual player for commercial use?

For the server side you can use Hyper-V Server 2008 R2. Depending on what your desktops are running Windows 7 Pro/Ultimate includes an updated version of Virtual PC. If you can provide a little more detail, like what OS you're planing on virtualizing in the server/desktop we can probably tailor the answers a little better.

If this is commercial use, do yourself a favor and buy a license for VMWare Workstation and be done with it. The extra features beyond the basic player will be appreciated.

I wouldn't invest in Virtualbox now that Oracle is behind it. When it was Sun, I had no problems, but I wouldn't trust anything with Oracle's name on it.

Virtual PC is fine if you're just going to virtualize XP inside Windows 7, but if you want to run Linux VMs you're going to want something a little more vendor neutral and robust... like something from VMWare.