Loads of stuff happening. This year (07) is the Highland year of culture, but next year will be just as good.
www.highland2007.com would be good to get an idea. Truth is, there are always things happening in the highlands, but maybe nothing much on the scale of the Edinburgh Festival.
August is traditionally the month for the Agricultural shows - google for the Black Isle show as a biggie, and maybe the Highland Field Sports Fair at Moy as a small but nicer day out (actuall, it's over two days.
July is the run up to this, but there's still things happening, and we have Highland games throughout the summer as well.
If you could put your stay off for a month or so I'd commend that though - Highland weather is traditionally at it's best toward the latter half of the summer months - July / Aug
should be better than June/July, on average.
That said, we have a saying here that if you don't like the weather then just wait ten minutes for it to change - four seasons in every hour !
Whatever happens, enjoy the relaxed pace of life and spectactualr scenery - don't plan on doing too much in any one day and take a chance to chill out with the locals - we're a friendly bunch.