To enlarge an XP Pro hard Drive on ESXi, do the following
Increase hard drive space in a virtual machine using free software (NOT) called VMware vCenter
HowTo: Expand Windows XP C Drive in ESXi 5.0 vSphere 5.0

My whole reason for doing this was for Quick Books 2006 and I ended up formating and installing everything fresh on the server!

1) create a backup folder (a folder called backup will do)
2) copy the folder of the current working machine into the folder called backup

side notes:
a) You must copy the folder to another folder hence the backup folder since ESXi will not allow a copy of the same folder in the root nor will it allow you to change the name durring the copy.
b) To get to the system's folder, you click

a) in the inventory view, you click the datastore at the top of the coloumn on the left, usually the ip number is the name of it.
b) on the right is a menu, click on configuration
c) under configuration is a much longer menu, click on storage (this is on the left, in the menu going down the left side)
d) on the right you will see a disk symble and it will say datastore1

3) while in the backup folder, rename your machines copy folder's name (even add a number, just make it different)
4) copy this folder to the root folder

Side notes:
a) if you do not know how to copy a folder, it's simply right click on the folder name (in the right side view because they are listed in the left and the right at this point) left click on copy
b) then when you're in the folder you want to copy to, right click in the open space of the folder and left click on paste

5) Start this VM, when asked if you copied or moved, "You Moved it"!  Once started, shut the machine down.
6) edit this machine.  delete it's hard drive.  add a new drive the size you want the machine to be and click on "independent and persistent"
7) in your old smaller machine's copy, edit it's settings and add a hard drive.  existing drive and browse for the new drive of larger size and set it "independent and persistant"
8) close settings, reopen and add your CD rom, iso file to your favorite drive partition editing tool (like gparted-live cd).
9) change bios of the VM to boot to the cd rom.. 
a) start the machine, hit f2 for setup, far right is boot options, click enter on the CD rom and shift plus to move it up, then f10 to save!
10) boot to your favorite drive editor, and clone the partition as a primary to the new drive and of the same old size (not larger yet!)
11) after cloning, start the new machine again..  it will start normally and windows will want to reboot, let it reboot as it sees the new drive sisze yea!
12) boot back to your drive partition editing tool, change the size to the size you wanted, save, then restart the machine again
13) when windows boots up, it will want to reboot yet again, let it and your done!
a) if your windows doesn't boot but rather your iso, simply edit the machine and either remove the cd rom to boot to windows or add the cd rom as iso and point to your iso file.. 
b) getting the iso up to ESXi is another trick. 

1) create an ISO folder
2) left click once in the open space of that folder
3) above a little bit is an icon menu and one will have an alt tag that reads upload, click it
4) browse for your iso file and click open and wait for it to upload!

If you have comments to add to my instructions, please use the contact form and send your suggestions to me with name / state so I can give you recognition for your contribution