If you've downloaded a trap file from a vendor site such as cisco, you can do a "xnmevents -merge 'trapfilenamehere'"
if you've got a few systems that you that you want to keep in sync (I've got 14 boxes running NNM6.31).. load up all your mib's and get the events setup like you want them, then;
copy snmpmib (ascii), snmpmib.bin (bin) to the new box(s),
mv trapd.conf -> trapd.conf.orig (or whatever you want to call it), then copy over the trapd.conf from the system you loaded the mibs on, next 'xnmevents -merge trapd.conf.orig' (or whatever you called the backup file).
This saves alot of time and headache trying to keep which evenents you've added/modified even accross the board.
hope this helps.