I have 4 x IBM 330 and recently where down unexpected. It turns out that where overheating or was too hot in the rack. I want to install IBM Director but I do not understand exactly the relationship between director and agent. Also do I install IBM Director in all of them or only one?
This isn't quite your direct answer but I'll try and tell you my experiences with IBM hardware and diagnostic monitoring. I don't run director (xSeries 345) as I'm running FreeBSD on my box but one thing that has been indispensable has been their Remote Supervisor Adapter II card. It is a PCI based LOM (lights out management) card - it has it's own network port and IP address and then you can log into it and do reboots, etc. You can remotely add disk images, too, and see a web-based video display of what the server would show to a local terminal (the card looks like a video card to the server and sends out compressed images via the web interface.) It has diagnostic info like temps, voltages and fan speeds. The card can independently email alerts regarding diagnostic failures. I am pretty sure you can daisy-chain the cards together and use one to report on muliple cards.
There is an older card, the RSA, as well. It has most features w/o the remote image mounting. They can be had for under $100 on eBay (the RSA I). The newer card is usually $150 or so.
These things have been a great asset, you may want to check them out.
I believe you can install the Director on one server and then just the agent on the other 3. That way you can monitor them all from one server. At least one of your servers has to have the full Director install.