If you compress files to save space Vista will also compress the bootmgr !
This means that you can no longer boot it up! very clever, only Microsoft could make such a dogs dinner of something like this.
I also then experienced problems making the computer boot from CD.
I finally managed this and used the repair facility on the Vista CD, it assures me now that Vista is working fine.
However when I try to boot up I get this message

Caution: This hard disk may be infected by virus!

Thats it I can't go any further.
Does anyone have any ideas as I am completely out of them.
Any help would be massively appreciated as the thought of losing everything in a complete re-install is unthinkable. Thanks in advance.