What power conditioners can convert 230v to 120v?

Vamrhein,
The biggest problem you will run into is the power frequency.
Australia power is 50 HZ.... Check the US equipment, if it is not 50/60 HZ rated you could find the equipment is not a bargain after all.

60 HZ only power transformers will hum louder and fail in time due to excessive heat if connected to 50 HZ power mains. Equipment with motors in them may run slower.

Try to avoid "converters". They are usually cheaply built autoformer-based. rather than a true transformer. If you do require a step-down transformer, check out used items on Ebay. I just picked up a regulated one for $29 that would have been over $1200 new and their lifespan is often decades. You would need to know the maximum amp draw of the components and multiply by 2 (roughly).

Jea48, not so in my experience. Frequency is generally not a problem at all, except for some TT motors of course. On the other hand my experience supports what Ngjockey has to say. However, if I were in your shoes Vamrhein, I'd sticK to Eldatford's advide as closely as I could.

Jea48, not so in my experience
05-15-09: Detlof

Quote from Link:
7. Noise
Transformers make noise. This is not only the electrical noise that is created by the nasty current waveform through the windings, diodes and into the filter capacitors, but actual audible noise. One source is winding vibration, due to the wire moving because of the magnetic field and the current flowing through the conductors. This is to be avoided at all costs, since constant vibration will eventually wear away the insulation, the windings will short circuit, and the transformer is ruined. Fortunately, this is rather unusual, but it can (and does) happen on occasion.

Most of the noise is from the laminations or other core material, which contract when subjected to an intense magnetic field. This is called magnetostriction, and happens to a greater or lesser degree with all magnetic materials. A stethoscope will verify the source of the noise, and there is little or nothing that will stop it. A resilient mounting will stop most of the noise from being acoustically amplified by the chassis, and generally the noise will be worse at no load. In some cases, a transformer may have been designed for 60Hz, but is used at 50Hz. In this case, the flux density will probably exceed the maximum allowable for the core, and the transformer will get much hotter than it should, and will almost certainly be a lot noisier as well. Toroidal transformers will generally be much quieter than EI laminated (i.e. conventional) types.

Most(all?) transformers designed specifically for 60Hz will eventually fail with 50Hz mains, due to overheating. The reverse is not true, and 50Hz transformers can be operated quite safely on 60Hz.
http://sound.westhost.com/xfmr.htm#7-noise

I've read two similar but different things about using 60Hz transformers on 50Hz. One wrote that the transformer should be derated by 17% to 20% (50/60). The other wrote the input voltage must be 17% lower than the maximum rating.

The latter being from: http://www.solaheviduty.com/support/faq.html

The Sola portable (120V) I do have is quite noisey, but probably not indicative of the type or brand. With hard wired ones, there have been effective installation options.

Sola is one of the few I've seen offering 50Hz models (group IV) in both general purpose and regulated.