Don't try to remove a snapshot in the datastore browser!!! This will break your VM, i.e. you will loose all current changes!
You can identify VMs with snapshots by checking their current virtual disk name as it shows up in the VM's settings. If the name is something like <vmname>-00000x.vmdk, then the VM runs on an active snapshot. You may also want to take a look at RVTools, which provides an excellent overview of your virtual environment, including VMs with snapshots.
André