networking question

i have windows nt 4.00 loaded at our office on compaq server . we have 45 user connected to that server . our client are loaded with windows 98 second edition . we also have oracle 8i loaded in the server . our client user compaint that they get disconect from the network access when they are idel for some time . what we are doing at persent is shutdown the pc and rise it again . it works normaly . so pls give a solution for this problem .