Well, as OE 6 is not supported anymore, any compatible program with XP that is newer and still gets security updates will be worth your time and troubles all the better to avoid issues with OE 6 getting exploited or hacked. Thunderbird will fit the bill nicely. Version 31.0 is the latest version, but at least SP2 is required, SP3 preferred.

Full Download Link: https://www.mozilla.org/en-US/thunderbird/all.html Choose the location that best applies to you.

As to Premier vs. AIS: http://www.avast.com/en-us/compare-antivirus More features, but pretty much the same as AIS in protection.