Providing that the user has a clue, a linux virus is not as serious as a win32 virus. Logging in as root will make the whole system vulnerable, whereas a login as a retricted user (like most of us use) only kills that one account at worst.
Some "viruses" are for linux, but mostly worms and trojans. Rare, but do exist. Just practice safe computing, run fprot or cheyenne and youll be fine.
Note, cheyenne and fprot are the only Linux virus protection suites available that I know of.