You should install .NET framework from microsoft:
http://www.microsoft.com/downloads/details.aspx?FamilyId=333325FD-AE52-4E35-B531-508D977D32A6&displaylang=en
and if it still doesn't work, try to also install the service pack:
http://www.microsoft.com/downloads/details.aspx?familyid=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en
Let me know how it works, I'm interested in how TieCal works with
Office 2003 (have never tried that myself - I use 2007)
-Isak