holidaying in september would like some ideas on a drive from las vegas to palm springs to san diego and the to la any tips on car hire hotels sightseeing etc from sydney australia would like to make the most of this trip 7 days available thank you

Nearly all fo the car rental companies are at a single facility in Las Vegas. There are regular shuttles from the airport to the rental facility. Rental cars are somewhat cheaper in Las Vegas than in California.
For a more scenic trip to Palm Springs, try going all the way across the Mojave Preserve from Exit 272 of I-15 south through Cima and Kelso. Cross I-40 at Exit 78. When you reach the National Trails Highway you will go 6.6 miles west to Amboy. The National Trails Hwy is the old Route 66. In Amboy you turn south eventually coming out at Twentynine Palms.
Route 62 will take you very close to Palm Springs.

Las Vegas. I you plan to see a show, book your tickets early for best seating. Cirque du Soleill is one of the better to best. Use this web site for all shows.
http://www.vegas.com/shows/

8 days?
I'd skip San Diego unless you want to visit Tijuana, Mexico.
Long drive. Palm Springs- eh. Superb golfing town with very good restaurants. That's it.

Otherwise drive from L.V. and spend the rest of the time in LA. An interesting route would be through Death Valley.
http://www.nps.gov/deva/index.htm

No Bondi Beach, but they are very good. Disneyland, Universal Studios, Hollywood, OF COURSE weird Venice Beach,

Skip San Diego - and get stuck in LA traffic? Surely you jest.

Also coming from Vegas to Palm Springs - check out going through Lucerne Valley.

FYI - from LA LA land to San Diego is about two hours - and then you can really enjoy how to appreciate Southern California.

Also - from Palm Springs to San Diego is about two hours - and a scenic - mountain drive is up the hill from hiway 111 - on 89? - toward Anza and then to Temecula and down I-15 to San Diego.

Oops. That's up 79. It has some curves - but quite scenic - especially when compared to going through Hemet and down to SD.