Win2k Pro file server question

We have a windows NT server (domain controller)running Back Office Server and a NEW file server running windows 2000 professional. We are running into problems with the 10 user limit on the files server and are wondering if there is a workaround forconnecting to the files on the win 2K Pro system THROUGH the NT server system. If not can we upgrade the win 2k Pro file server to win 2k server without losing our data?