What email program do I choose?

I have upgraded my pc to windows XP, when I had windows 98, Microsoft outlook worked fine but with XP it now wants the original CD to load something or other - I dont have this CD (it was illegally installed on my pc), outlook express also will not work (I think because it is also made by microsoft - it also asks for the CD) so I downloaded incredimail xe from the net - it seems to work ok but there is one huge problem, since I have one email address (on one email server) when I installed incredimail it installed a seperate inbox for each of my user accounts (1 administrator and 2 users) I have tried to fix this and cant. This is a pain because since Im not connected to the net all the time, when I download my emails that only appear in the 1 user account that was asked to check the email. I am currently battling with task manager (it will not start) and I think its incredimail that is causing this. I dont want to uninstall Microsoft office since Word, Excel and Access all work and I use them, I am thinking of uninstalling incredimail and downloading another email program from the net - but I dont know which one to choose, I have used pegasus before and I hated it - very difficult to use. Does anybody think that reinstalling XP will solve my problem with task manager, also if I reinstall XP will I have to reactivate windows? Advice advice advice PLEASE!!!