splitt inet from the rest..?

Hello, hope that I can bother you with a simlpe question. I would like to make sure that my internet actions can not hurt my system. Would it be helpful when I create a special user for inet and email? Would that help at all b/c this user is in the group users and this group still could hurt my data (ever when I am a different user) or? What would the experts suggest how to setup a system where my private data is save ever when I use the internet and email? I am running SuSE 8.1 with an analog modem and have a callback connection to a differnt server. Thanks a lot for any hint. Michael