HOWTO use the Laserjet 5si
The printer is an HP Laserjet 5si MX. It has a built in JetDirect card, so there is no external networking equipment. The printer's IP address is 10.13.0.51
On a Mac, this is pretty straightforward. Just know that "port 9100" is the protocol to use, and if it gives you a choice between PS and HPGL, either should be fine.
On a Windows box, you need to ignore the temptation to click "add a network printer", and instead, "add a local printer", then "create a new port", then port type "standard tcp/ip port", then enter 10.13.0.51, and everything else should be sensible. If you are using Windows 7, there is no driver specifically for this printer. There should be a built in driver for the model (Laserjet 5si MX), ether version (PS or non PS) will work. If not, drivers for the Laserjet 4 should also work.
On a Linux box, CUPS will have drivers for this printer.
If things aren't printing, don't just randomly mash buttons on the printer. This is silly and likely to waste your time, and annoy the printer. Instead, see http://h20000.www2.hp.com/bizsupport/TechSupport/SupportTaskIndex.jsp?lang=en&cc=us&taskId=110&prodSeriesId=25478&prodTypeId=18972 and try to actually troubleshoot the issue.
Please don't change the printer's IP address or configuration, it is not at fault. Seriously. Don't do it.