From a previous business, I have 5 Dell Poweredge 2850 Servers, each with 2 Intel Xeon 3.4 Ghz processors. I also have 2 2950's, a huge 7150, and few other smaller 1 U Dell servers. All but 2 of those machines are just sitting there in the rack and not even turned on right now. I have seen CPU miners and know that these are not optimal, but have considering making 5 mining servers out of the 2850's to just see what happens. My power bill increases around $400 a month when running all of these servers/switches/UPS/Firewall/etc. (more in the summer than winter of course). I have all the infrastructure and hardware to setup these machines, but I can't seem to find any data on potential earnings with Xeon processors to see if it would be worth my time or the extra power to build miners out of these machines. I understand that with the difficulty going up the earning will continue to decrease, but if anyone could provide some rough potential numbers or suggestions for further research, it would be appreciated.
Two or three years ago, yes, you might've mined some BitCoins with this equipment.
Now it's all obsolete, compared with ASIC-based equipment that outclasses it by 3 or 4 orders of magnitude in hash-specific processing power.
You could run all your current equipment for a month and probably not even mine a single coin.
If you could get recent GPUs (Radeon HD 6850 or newer) for very, very cheap, you might be able to make a couple of Bitcoin per month. It may not be worth it, depending your electricity costs.
Use these tools to help guide you to an informed decision:
vanitygen is probably your best bet given the equipment that you already have.