I grew up in Altona, but now live in Werribee. I can recommend a great vet there, as long as you don't think the drive is too far.
It's the Hoppers Crossing Veterinary Clinic and Hospital at 5 Barber Drive Hoppers Crossing. Their number is 9748 6644 and website is www.hopperscrossingvet.com.au
They are only about 2 mins drive from the Plaza.
They were recommended to me by a neighbour who has been using them for over 15 years and I have been using them for 3 years now. Though it has quite a large staff, it is still small enough that you always feel welcomed and the receptionists eventually get to know you really well.
They are open into the evenings (esp. important if you work) and it is always possible to get in if there is an emergency.
Failing that, I think the best bet is to ask local dog owners. The Agility Dog Club of Victoria meets at Crofts Reserve on Blackshaws Road (Grieve Pde end) every Friday night from about 7pm. Maybe pop down and ask a few people for some recommendations.