backoffice small business server

I HAVE TO UPGRADE AN EXISTING SERVER RUNNING BACKOFFICE SMALLBUSINESS SERVER ON A PENTIUM 300 SINGLE CPU TO A NEW SYSTEM WITH TWIN 700 PENTIUMS WHAT IS THE EASYEST WAY TO TRANSFER ALL OUR DATA,FILES POSTOFFICE EXT AND TRYING TO KEEP THE NEW SYSTEM AS CLEAN AS POSSIBLE AS I BELIEVE THE TWO MACHINES CAN NOT BE CONNECTED ON THE SAME NETWORK. A TAPE BACKUP WILL TRANSFER ALL THE JUNK AS WELL