I'm not sure that you can use 2 profiles in the same XP user account. At least not without it being a complete pain in the neck...

I assume that using one ThunderBird installation but with 2 email accounts in it is not something you wish to do? Here at home, I run only ThunderBird. I have 2 email accounts on this PC and 3 on the other one, but all under one user and one installation on each PC. The only thing I don't have is complete privacy between the individual email accounts.

Of course, if you set up another XP user account, setting up another ThunderBird profile is very easy.

One last semi-unrelated opinion. Why would you run such an old version of ThunderBird? Several of the recent updates were due to security issues. IMO, running an older version could be putting your PCs security at risk...