Aren't the biggest factors here the budget and how many computers you need/can fit in?

I'm not saying that we're dripping in money or anything, but we've got more than plenty of equipment money budgeted for this. We're more constrained on space to fit the machines than in the capital costs of purchasing them.

It's 'only' a student lab. Spend the bucks on a decent server box. the next big thing might be the service contract you'll get with what option.

We've got a machine room, next door, with lots of loud servers and experimental hardware (the biggest box is an Alpha with some 10GB or so of RAM). The point of this particular lab is to create a comfortable space where people want to go to work together. As a side effect, if we can make it comfortable for hanging out and having spontaneous meetings (with the poof chairs) and useful for practicing talks (with the video projector), then that's all the better.

I expect that half of what these machines will do is run LaTeX, PowerPoint, and similarly non-demanding tasks. Of course, we do lots of peer-to-peer systems research here, so the gigabit ethernet and spare hard disk space will likely get put to good use. (Dell's OptiPlex machines all come with gig-e built in, just like Apple's machines, so why not use it?)

Who signs the check for all this? What is the lab for? If it's experimenting with hardware, don't spend too much on it. Can you give some more information on this project?

The checks are being signed by me and one other professor. This is meant to be a general-purpose user-friendly lab, thus the emphasis on nice monitors and quiet machines.