Verbs

What's the difference between a verbal aspect and a tense?
As I've concluded, an aspect includes the various odd things you might
want to tack onto a verb, whereas a tense is strictly a place in
relative time.
Would it be feasible for a language to have tense based on a definite
event or an event defined at the start of a conversation, where actions
occurring within a certain duration of the event are present and others
degrees of past and future depending on their distance from the action?
This sounds like another of those stortelling culture features, where
perhaps it's traditional to start a story in the present in the middle
of the plot, and bounce back and forth in time as the story progresses.

Also, is there precedence for inflection patterns dependent on word
origin, or is that too artificial?  I was considering having words
native to my language inflect with case suffixes, and use prefixes for
obviously foreign words, or words that the informal register allows but
aren't used in polite conversation.
--
-Shreyas
Loth 77
http://elfwood.lysator.liu.se/lothlorien/artists/ssampat/ssampat.html