Powerdown the VM's and then the esx host
Add the new drive physically.
Boot the machine in bios and check that it recognizes the drive
boot the machine and open your VI client to that machine
Select the machine itself, tab configuration
Select Storage
If the new local storage is not yet visible, in the upper right corner it has a button "rescan all"
This should list the new device.
Adding a new drive to the VM, midnitesnake has that set up.
Or move the VM to the new storage (download + upload)
edit the vm, select the disk you want to extend and enlarge it.
Note, this will not automatically enlarge the disk in the VM itself.
Use diskmanager to enlarge/extend the disks.
On W2003/XP its harder to extend the systemdrive, use Dell's Extpart for that
Pm me if you have any questions