Calculating weights in a particle filter experiment using multiple state variables
No, it's not a stupid question.  Reweighting (or resampling) particles is non-trivial for any "fun" problem.  Weighting is typically performed by computing the likelihood of the particle fitting the observation.  See page 28 here.  This link and this link give reasonable discussion on particle resampling.

These links assume you can easily compute the likelihood a particle corresponds to the observations.  For ease, we typically assume the likelihood can be expressed as a normal distribution (i.e. with a mean and a variance). Since your observations are comprised multiple dimensions, you might use the multivariate version of the 
normal distribution.