This is an indictment of the OS, not the computer. Remember how VIsta was so slow compared to XP, driving people to use circa 2008 Linux distros to wake their machines up? You can still find disk images for older distros, and there are distros tuned for older machines as well. For years I've suspected most computers need to use an OS no older than they are, yet no more than 5 years newer as well. Used to be ten years for Linux, we are slipping in that regard. I think we are having a "vista moment" with current X drivers and DE's.
As recently as 2008, a Pentium 4 or Athlon Thunderbird/Athlon XP found on a curb or in a dumpster was a real treasure for some of us. For years I did audio editing on Pentium III's and a 500MHZ early Athlon, those were what we got for free from 2002-2008. In 2008 my crew had a whole bunch of PIII's set up in a community center for free internet access. Compared to these, a Pentium 4 was and is damned fast. I've never had a "too slow" complaint from a friend I gave a 1.4GHZ Pentium 4 laptop with Ubuntu Karmic on back in 2009. Yes, it had crappy graphics, no, it doesn't run Compiz or need to.
The only Pentium 4s that are power hogs are the Prescott chips, you'd be amazed how small the heatsink on a circa 2002 Pentium 4 can be compared to the huge towers needed on today's big 4, 6, and 8 cores. Of course, these modern machined to different jobs than P-4's were designed to do, such as HD video editing.