On using Word 07 vs. Word 00: if you install Office 07, you shouldn't have any problems opening your old 00 files in it. It has compatibility with older versions. Now, to make sure that you would be able to open a file created in Word 07 (for example) on a older version (97 to 2003), all you have to do is "Save As..." and select "Word 97-2003 Document". You might be confused at first with Office 07's style and organization of menus, but I think it's easily adaptable.
On antivirus/spyware/etc.: I personally use AVG Free Edition as my antivirus, and also have free ZoneAlarm firewall. I think that, as long as you are careful with what you download to your computer or which webpages you open, having (malware) problems with your computers is very controllable.
malu
