They might have met when him and Nappa attacked earth or when him and her were at Namek during the freiza arc. Then again, it could have been a idle time and they just met and hooked up and out popped Trunks. :)

i think goku met her when when goku first started searching for the dragon balls and bulma used her dragon ball detector to find them too she bumped into him

Vegeta was training using the gravity multiplying effects of the machine in the spaceship Bulma made. So he was spending an awful lot of time around their house, he probably saw her every day. Something obviously happened during that time but they never really explored the specifics of it.

They never really had a relationship, I think both just got really horny at the time.

i'm not sure, but i know they had a kid together

Vegeta and bulma were almost perfect from the start. since dragonball, bulma has always been a fiesty, aggressive female, and in dbz/other times bulma shows she is into aggressive/often jerkish behavior for its "manliness" in a sense. In huge periods of time Vegeta and Bulma spent together, vegeta saw that you could be tough and still have a soft spot. No one else showed him this side because most people are >too< good in his views. Thus, vegeta was hooked. Bulma was exactly looking for that, the manly aggressive type. (which, she also complains about affectionately, and is truthfully shocked and hurt when vegeta does things like blow up the stadium in the buu saga, and refuses to believe that that is >really< him.) thus, trunks appeared. This is not the >outcome< of their affection, it is an event that confirms and solidifies their bond. Vegeta mentions this when he is about to fight buu when he arrives at the first scene.(also when he blows himself and a huge crater up.)He states "I actually grew soft, fond of them even." And we know that as he sacrifices himself that time that that is who he really is underneath, he's good. I'd love to talk more sometime ^^) cheers.