Building Linux Appliances - Dealing with Heat Issues?

wyrfel asks: "I'm going to build a router & switch based on LRP on the software side and on a FIC PA-2005 with Pentium 200 on the hardware side. Having read some discussions and wanting to make the system as quiet as possible I've remove everything except the floppy (which will be removed once the system is up an running), CPU and RAM from the board, lowered the boards speed from 66MHz to 50MHz which brought down CPU speed to 150MHz, did cut of the power supplys fan and lowered voltage of the CPU fan to 5V instead of 12V. So far everything seems to work fine. The power supply gets a bit warm on the top but it seems to be ok. I didn't add any PCI / ISA cards yet, so I wonder if doing so would bring problems through higher power consumption. What I really worry about is the heatsink that is placed directly beneath the CPU heatsink and that gets a bit hot when running the CPU fan with 5V. With 12V it's fine because of the extra airflow that comes from the fan located near that heatsink. BTW it is attached to some tiny piece labelled 'LINFINITY LX8382A'. Can someone tell me if I have to worry about it becoming too hot and if so what means 'too hot'? Any hints or further suggestions?"