For the most part, yes. Except Win98 != WinXP. WinXP is still actively patched when new flaws are discovered (albeit slowly).

A few tips.

#1 - EDUCATE YOUR USERS - most important factor by far
#2 - Deny All, then allow only the required users/services
#3 - Update, Update, Update. Your Virus/Malware/Adware/etc protection is only as good as your last threat database. New threats are discovered daily.