I'm sorry about your loss, lisalularsen.

Your little gnats are known as "fungus gnats." Here are some previous discussions on this forum:
http://search.gardenweb.com/search/nph-ind.cgi?term=fungus+gnats&forum=terrarium&forum_name=Terrariums

and a fact sheet on fungus gnats:
http://www.ext.colostate.edu/pubs/insect/05584.html

However, it would be good to know exactly what's growing in your terrarium before you decide to let the top of the soil dry out, etc., so if you're not sure what they all are, it would be a good idea to post photos of the plants for folks to identify. This forum isn't too active (I followed a link here from the "recent posts" on the right side of the page), so you'll probably get quicker IDs by posting the photos in the House Plants or Name That Plant forums.

I'm sorry for your loss.

When my globe terrarium developed fungus gnats, I sprinkled the surface lightly with a granulated product containing BT (bacillus thuringiensis) that I keep on hand for use in the bog next to my koi pond. It is safe for plants (and koi, obviously, as well as pets and humans), but corrected the fungus gnat situation very quickly.

They're fungus gnats. Harmless but can be annoying to look at. If you seed the terrarium with springtails they'll help control their numbers and possibly wipe them out as they both compete for the same food. Springtails stay close to the soil so it would be better for the terrarium if you don't want gnats ruining it. Both species are beneficial for the terrarium, it's just one is not very nice to look at.