Let's see some of the old machines that I still use:
2 identical Compaq PIII 500mhz BX machines that I use for Firewall, 1 is for backup if the first one ever fails (which it never does). Then I have 2 more Compaq PII 400 - 450s with BX chipset. Fail proof.
1 dual PIII 733 HP 768 MB RAM Netserver E800 with 2x U-SCSI-160 + Adaptec RAID card as a Linux server with Debian.
1 PIII 500 @ 560 in ASUS P2B + a lot of cards like scsi or such, runing Win 98SE, should I need that.
Tons of old slot PII 300-450 Mhz as spare parts + Socket 7-9 mobos and some P133 - 233MMX CPUs.
I actually have a CPQ P200 classic as a LRP Printer server hooked up to a HP LaserJet 4MP.
Also a Dell P3M 1Ghz Inspiron Laptop that I use to watch TV-episodes, chat, skype and surf with in bed. (Best laptop I've ever had, dropped it, spilt loads of water on it, still runs perfectly). Only thing it lacks from being perfect is ~ 2.5 Ghz dual core cpu, USB and Wi-fi built in (I have 2 PCMCIA cards for those things).
4-6 Socket A/P4 which is newer, but no one of them will even start, or go past BIOS post, because of the crappy ICs and components of the mobo. Anno 2001 - 2003, MSI, ASUS, ASROCK, they have all become defective over time.

So now I have 2-3 spare Athlon XP 1700 - 2500 and tons of DDR dimms that wont be used.