My client has a Mac Pro with 9GB of memory, 3 7300GT video adapters and 4 Monitors. He is running Parallels 3188 and is using parallels in the Boot Camp partition. When he starts Parallels and then boots XP he gets a Parallels login dialog which he is able to dispatch by pressing the enter key. He then gets the loading Parallels Tools warning and Windows starts normally. Due to instabilities and lockups with OS X when running the XP virtual machine I advised him to start the XP Virtual Machine in Safe Mode and uninstall Parallels Tools. Then to start the XP virtual Machine normally and install Parallels Tools. Unfortunately, Holding down the F8 key does not bring up the XP startup choice screen. I do not have this problem with my Max mini running 3188, but I do not have boot camp installed.
This is a Mac Pro not a Mac Book. There is no fn key. Holding down F8 on my system that doe not have boot camp installed works just fine.