Bring beer to boil.  Reduce heat.  Simmer kielbasa in beer for 15 minutes.
In separate pot on med, heat, mix together:  ketchup, mustard, brown sugar, vinegar.  Sauce will be thick and dark red.
Drain kielbasa.  Cut into bite-size chunks.  Stir into sauce.

At this point, I usually transfer the mixture to a crockpot and leave on low throughout the party.  The longer the kielbasa sits in the sauce, the better.

Serve warm.

This is an excellent party/buffet dish, SO easy to make, and goes a long way.  The recipe can easily be doubled for larger crowds.  When I serve it at a party, I throw it into a crockpot (on low) to keep it warm.

Send me PM if you have any questions about this recipe.  -Deb