slow samba with nfs

Hi everyone. Our AMD 1100 box serves a samba lan of 22 machines, some 7.3 and some w98 in a small international school. Some of the 7.3 boxes are not samba but take files via nfs. If any of the 7.3 nfs's are logged on, the samba clients slow down noticeably. This is particularly apparent when everyone wants to access the same file, e.g. at the start of a lesson. Any ideas anyone? Thanks, Steve