First step in any major upgrade is to obtain an external HARD DRIVE and make a full back up (Image) of your existing drive using CD based back up software such as Acronis True Image (What I use) or many many many other programs that are just as good.
THEN you upgrade, IN theory you will loose nothing in the upgrade, but if you do.. RESTORE from backup and do not upgrade again.
If you loose something like Office.. Try Sun open office.. I like it better anyway.
And whatever you do get GOOD Anti-virus and good FIrewall, DO NOT Trust a router to protect you.