If you change from XP to Linux you won't *need* a security package...
The only reason malware/crackers are rampant nowadays is bad practices from microsoft, even if there were any viruses on Linux, AND you were a "Typical" windows user, it would still take a lot of very specific steps to get a virus to work (Including password, permission changes, etc)
Firewall, antivirus, antispyware, antimalware in general is not necessary and sometimes just makes your system more vulnerable...
@Colanth: No, but there is such a thing as an operating system that does everything it can to enable malware of all types which - having the majority opinion - distorts everyones concept of "Immune" - put simply, viruses only work because so many computers are already compromised (By windows)
@Bull: Another typical "If it costs more it's better" argument... Go buy some expensive fake security suites big mister "Security consultant"
@Fordry: I'd stay away from firestarter... runs as root, hasn't had an update in 5 years, conflicts with ufw (Installed by default on ubuntu) - clamAV does the job but it's manual scan only... But then all you need it for is sending risky files to other people anyway...
@UK_PC_Tech: Agree on antivirus, but linux is not in "Development stage" and there are many articles on it's virus quashing abilities...
@OP: As you can see, you hit a touchy subject... IMO you should just google some of the articles on why you don't need/shouldn't use the above on linux, much more in depth...