Sadly they plugins won't work in Max 6, they were compatible with Max 3, 4 and 5.
If you can track it down the freeware Gmax is an option (I had a peek, it looks like you should still be able to get it through TurboSquid), and you could also try Milkshape. I can't recall if there were any issues using Gmax, but I know Milkshape had some limitations, such as inability to set up dummies for hardpoints and damage points, and I think making break models was also difficult.