Its an interesting subject but I am not totally convinced as you can see here;

http://www.thegardenersalmanac.co.uk/Data/Companion%20planting/Companion%20Planting.htm

Marigolds (calendula) near tomatoes works because aphids prefer marigolds (and nasturtiums) to tomato plants, particularly blackfly.
I don't grow veggies, but I have just planted Viscaria (catchfly) in an area that suffers from capsid bug in hopes they'll get stuck on the Viscaria and thereby reduce the numbers.

Companion planting does work, you just need to know which plants work with what. Rather than me typing in all the info again copy and paste this link into your web browser (not Google!)

http://bit.ly/HSs66O

You could also consider using garlic spray to deter a lot of the beasties.

I did a blog on Companion planting 28th April 2010. You might like to read the replies I got. It was gleaned from The Ken Muir website.

Gosh I'd forgotten that Scotsgran it was an interesting blog too!

Thank you Mg.