@fire: it depends on the job. actually, what cot said is not new to me at all. if you apply for a job you are overqualified for (or you are clearly going to be overqualified for in a short while, because you're going to get further education) there is a strong probability you won't be hired, because employers tend to want dunderheads in dunderhead jobs, and smart people in smart jobs. this happens for two reasons: one, dunderhead jobs are often slightly underpaid and those working in them might be also slightly abused by their bosses, and while the typical dunderhead does not complain, possibly the smart person could raise a ruckus and diminish productivity. two, if the bosses need to have someone to fill the place for a number of years (which does not happen often in this day and age, but it might still be the case), they don't want said person to get up and walk away as soon as they reach a new educational qualification. to sum up: good grades from a trade school are good for high-school level jobs, while good grades from a school that might lead to university are not good; they'll be good, along with university grades, for graduate-level jobs.
this is true if we're talking about the private sector. the public sector, on the other hand, favors overqualification in the countries where collective contracts exist and union activity is strong: the career steps are more or less fixed in an effort to grant everyone's rights, so nobody can be much of a troublemaker. also, the reduced competition also somehow brightens the mood, removing one of the reasons to embrace troublemaking itself.
@cot: what are your possible uni choices?