Shared folder has intermittent slow down

I have a windows 2003 server (just a member server, not a d.c., on a Windows NT 4 domain) in a marketing department with about 5 pc's (Win XP pro) accessing a certain share. There are 10 other shares on the server, each being accessed by each of the 5 pc's at any given time. The shares contain graphics for print and web. When accessing one of the shares, the "press" share, the connection will be really slow. However, this only happens to maybe one of the 5 pc's at a time and only on the "press" share. For the rest of the pc's, the connection to the share is perfectly fine at that time. It seems to be a different pc each day that has a slow connection to the "press" share

My thoughts: I do not think that this is simply due to network traffic/server load, since only 5 pc's are connected to the server and it is a 2.4 GHz Xeon with RAID 1 mirroring. It should be able to handle the load without any problem, even if we are using it for graphic image storage (only about 25 GB of images total on the server). The "press" share has about 1500 files totaling 1.5 GB. Also, if it were network traffic/server load, the other shares on the server would run slow too as well as each of the other 5 pc's accessing the server.

Please advise with any thoughts/comments.