Just make sure your install of DW is patched to version 1.04.
If your disks are old enough, you may have to find the patch and run it.
With Sub Command, you may want to install the SCX mod. You can find it at the other sub sim web site. SCX adds newer 3D models and expands the data base of countries and platforms. SCX is actually several SC/688i mods combined into one mod, think of it as a "one and done" type of upgrade.
As Chazly has already mentioned, Sub Command has more of a cold war, blue water feel while Dangerous Waters is based more in a post-cold-war era. DW has a slightly better "world map" (its more defined) to reflect missions in shallower waters. You may want to install both games in case one of them becomes tiring, just realize that SC and DW are essentially the same game.
