Like Dave said, nearly all the older PCs with a built in parallel port have address 0378 as default.
Most of my PCs are Pentium 4, 2.8 to 3.2 Ghz. I spent a whole week a few months ago getting about 8 PCs installed with Mach3, plasma profiles loaded, etc. When it comes to older PCs I can never have enough spare, too many have just randomly died on me in the past. Saying that I think a lot of the "deaths" were due to failing memory sticks.
On a side note, I seem to have got the best Mach3 drier tests with Intel motherboards. Can't remember if it was VIA or SIS chipsets that someone said are known to be problematic with Mach3.
Keith.