10.2 "Client" running as a file server

[lupus]

Well, my problem has been partially covered by lots of other threads, but still I dont know how to manage this properly:

We have a small 100 Mbit LAN with 8 Macs running OS 8.6 to 9.2.2 and a couple of Windows (mostly NT) machines. At the moment I have a beige G3 running ASIP 6.3.2 under OS 9.1. Fine so far, the throughput is good (6-10 MB/s), but ASIP tends to crash from time to time (200 GB RAID with half a million files on it). So I would like to have OSX doing the job as it might be more stable. I have the "Client" version of 10.2. I do realize that basically there is not much difference between the server and the client versions, except the GUIs in the server version that help to configure the services. I dont need the web, ftp, quicktime, mail etc. server things, just a plain file server. What I have complished so far is: install 10.2 on a dual 450 MHz G4, personal and windows sharing enabled (well that wasnt too hard ;-), and establishing different share points (using SharePoints) with guest access.
Now my problem (impression) is that OSX doesn´t deliver a constant transfer rate. No matter whether I copy to or from the server (I call it server now, allthough its running the client version), the copy process suddenly breaks down for a while and then resumes. The peak transfer rates are o.k. (about 10 MB/s). I can´t see why it would drop down frequently. The cpu usage drops at the same time, so no other processes seem to be responsible for this. I have been playing around with renice on the "AppleFileServer" process but that didn´t help either. Should I renice a different program/daemon? What other processes are involved in the file sharing service (Finder???), or how else can I improve file sharing?
I´m really rather new to OSX and an almost complete idiot as far as Unix is concerned. Thanks for any help, Andreas