There's actually a newer model out (or just about to come out) of the Polo; main diff looks to be the headlights - two round units on each side, tilted backwards, like on some Mercedes. See attached pic. Ugly IM(nsv)HO.
Other diffs seem to be mostly interior refinements like new instrument cluster, stowage boxes below front seats, foldable rear arm rest, keyable passenger airbag, etc...

A '99 Jetta should present any major problems as long as you know about the ISO pinning issue. I'd also assume it has the same sort of antenna as my Polo, ie. requires an adaptor so you can feed it power along the antenna wire.

/Michael