Namek. He and Zarbon follow Krillin back to where she is hiding. Krillin has a Dragonball from Guru, which Vegeta is after, and Zarbon is after Vegeta to kill him. In the end Vegeta defeats Zarbon and negotiates the exchange of Krillin's and Bulma's life for the Dragonball. Later on Vegeta meets Gohan, (who is on his way back to Bulma after retrieving another Dragonball from a lake near the Namek village that Vegeta distroied earlier) and Gohan notices the Dragonball that Vegeta has, and Vegeta tells him that he got it from Krillin and "that geogeous" girl he was with (English version anyway). So there you go lol, that was the first time he met Bulma (about episode 44/45), unless she was with the Z Fighters at some point on Earth when he arrived with Nappa, but I can't remember that. I think she was at Master Roshi's actualy, thinking about it.