I don't see a use for these... I mean if you want to runs something separate from other stuff, just install a virtual machine...
I have a nice p4 desktop with 1gb of ram sitting too, wish I could use it to make few bucks a day, but can't think of anything.
You have to think outside the box, no pun intended. I have 15 computers in my home office. ALL are doing something...
Albiet YouTube views, FaceBook, SenukeX, xRumer, whatever... there are definitely ways to use a computer like that.
Example.... go to u2bviews.com, sign up, then run the browser 24/7. Before you know it you will have 1,000's of credits. Create a video, upload it... apply the views. Purchase YouTube views from people on here of fiverr. Do a bit of work to attract even more viewers from FaceBook, Twitter, whatever... Get enough views and you might get profit sharing enabled. Or upload a CPA video, drive traffic to the video, then drive traffic to your CPA site.
Another: Run a Scrape program to find niche phone numbers or Email Addresses. Get a few thousand, then design a product/service that you can sell them.
etc... etc... etc...
There are SOOOOO many ways to use old computers, like I said, you just have to think outside the box. The people who tend to think outside the box, or think ahead... tend to be the ones who are successful. Knee-jerk reaction people, or people who don't know what to do.. are the ones who tend to be left behind. Make your future...