On certain maps when I try to join game, MW crashes to desktop with a box asking to put disc 2 into drive. It never happens with Mercs maps. Anyone have a solution?

The "disk 2 error" is a common error that you don't have the terrain files of these custom maps installed.
More info: http://www.ctftimberliners.com/Maps/MapProblems.html

Get the big map packs from MWL or NBT, this should fix most problems with custom maps:

MWL Map Packs or NBT-CDs

Hope that helps!