Depends on the virus, but many if not most will infect both partitions. A "good" virus will infect your hardware and anything connected to it by ANY means.
Better to not get one in the first place. Sounds simple, but you are already preparing for it. Get a good anti-virus (free is fine) MS Essentials is finally mature for 7 unless you want more hands on control. Be very careful what you click, there is alot of BS on the internet. Don't open random attachments until you confirm someone sent you something. If it sounds too good to true, or too bad to wait, it's probably a trick. Etc. etc. etc. just be smart,
Oh, ok, thanks!