Go for it, I had the kind of upgrade that test your nerves ("Continue manually" (read-Troubleshooting-ignore all restarting request from inside the VM), stuck in "Step 3 of 4" forever) and afterwards watching things run so slow you feel like pulling your hair and kicking yourself for not waiting longer to upgrade.
But amidst all this V4 behaved like a trooper after "Force Quit" several time, and every time I restarted it kept plugging away until finished the upgrading.
But this is what I recommend you do BEFORE starting:
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1- MAKE SURE YOU HAVE AN EXTERNAL BACKUP!!!!!!!!!
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2- THIS IS THE 2ND MOST IMPORTANT: make sure you have not upgraded lately to a new computer or hard drive, because this will bring the stupid: "... hardware has changed and XP needs activation", if you get caught in this, keep trying every time upgrade stops, "Force Quit" and restart until finished (no damage caused) WHAT DO YOU HAVE TO LOSE, YOU HAVE THE BACKUP, DON'T YOU?
3- Make sure you have your VM in "Autologon" (no password needed to log in)
(on Win XP, go to Start--->Run and type: "control passwords2" and uncheck something that says " Password needed to login" or something like it (top-left) and when asked for Name and password enter YOURS not "Administrator")
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WHEN UPGRADE IS COMPLETED:
Things may run slow and you may get "… not enough Virtual memory" and/or freezing of screen; things running SLOW, feel free to kill Parallels as needed and restart, and the first chance you have to open "Karsperky Internet Protection" (something like that) make sure you stop it from scanning, in my case I completely got rid of it.
Then you will be glad you upgraded!
Cheers,
Emilio