I use windows 98 because of one program. I also wanted to try Ubuntu for AMD 64 so I decided to upgrade to PD4. After install: Win 98 crash on startup. I guessed I should have removed Parallels Tools before the upgrade. I did a few installs from scratch after saving my important files with Parallels Explorer and discovered this: 1.The VM freezes at every shutdown if Parallels Video Adapter is used. It is necessary if one wants 800x600. 2.The boot sector of the system disk needs to be repaired once. Not sure if this is because the brutal shutdown. 3.I can actually use my specific application(TI Flash Studio) as long as I never reset the machine. That is: If I turn the VM off it canÂ´t be restarted(already sent 2 bug reports about this). The only method is to take snapshots and hope that a restart of the VM wonÂ´t ever be necessary. How come one single harmless installation can have such a lethal effect on a VM? (The application is a SDK for the TI-92+ calculator and can be downloaded at http://education.ti.com/downloads/files/computer_software/fsinst.exe ) IÂ´d be interested to know in anyone can use this program in other Windows versions as well. Thanks.