I'm seeing bursty transfer rates as well when copy large files to my NASLite box. From what I can tell, it looks like transfers go quickly until the buffer memory on the NAS box is exhausted, then pauses until part of the buffer is written to disk. I would bet that the transfer rate, when averaged over a long enough time span, would work out to be whatever the write speed of the IDE bus is.
Anyway, for comparison, here are the specs for my NASLite box:
P2 (Deschutes) running at 450 MHz
128 MB of PC100 SDRAM
Western Digital 7200 RPM 120 GB w/ 8 Megs of cache
Here's a snapshot of the network traffic from my machine to the NAS box. It tops out at around 10 MB/second.
Here is what the NAS System tab reports about the NIC:
RealTek RTL8139 at 0xc8800000, **:**:**:**:**:**, IRQ 10
Identified 8139 chip type 'RTL-8139C'
link up, 100Mbps, full-duplex, lpa 0x41E1
Link encap:Ethernet HWaddr **:**:**:**:**:**
inet addr:192.168.0.10 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:28268676 errors:5024 dropped:69986 overruns:4279 frame:0
TX packets:14666638 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:3238719337 (3.0 GiB) TX bytes:1023687483 (976.2 MiB)