Edit: Oops, missed raybob's post, But oh well, this may still be interesting to some.
Well, I thought maybe this was for computers you use from day to day, but if we're posting our oldest, I think I might win!
IBM ThinkPad 755C
Windows 3.11 for Workgroups
75 MHz DX4 Processor
7000KB RAM
2x PCMCIA slots
340MB HDD
She's a pretty slick little machine!