Building the GWA or vis data with separate tools seemed to fix some of my problems with crashing in DOS... it just takes awhile to build BSP\vis for larger WADs on my Pentium 120 - along the lines of 3 hours for TNT\Evilution. I was not using fast mode though because that appeared to be what Vavoom was using normally when I would get crashing. I still get crashes, but much less frequently.