quick way to check server physical or virtual machine

One of the fastest ways is to check by MAC addresses. If it starts with


00:0C:29 VMWare (auto)
00:50:56 VMWare (manual)
00:16:3e Xen

The VPS provider can change the MAC address ranges (in Xen at least) but most people usually don't bother. It's by no means a foolproof method though.
 
On Windows just open a command prompt window and type getmac.
The MAC address will be the column on the left (under Physical Address)
e.g.
C:\>getmac

Physical Address Transport Name
=================== ==============================
00-D0-xx-xx-xx-xx \Device\Tcpip_{GUID}