I was wondering about postgrad in the USA. I'm an undergrad in UK but I will finish with a masters and I heard that the US postgrad programmes make you do a masters as well. Is there anyway to avoid this? Also is there any financial support for doing post grads there? I should end up graduating with a first so grades won't be so much of a problems hopefully.
It's not that they make you do a 'Masters' as such, it's just that a PhD over there is typically 5-6 years long, as oppose to the UK 3-4 years. The first two years of a US PhD are largely taught, in contrast to the UK where you would just dive straight into research as soon as you start, and just have a few grad courses taught on the side.
I'm not sure if there would be any way to skip the first year or two, if you already had a UK MSc. I can't see why it wouldn't be possible if you could provide evidence that you enough credits and had taken the graduate taught courses already in the UK. I think your best bet would be to prospectivley email some departments over there, to get a definitive answer on that one.
As for funding, in the first year or two I think US postgrads are largely supported by teaching assistantships (TAs), which typically involve around 20hrs a week teaching undergrads, labs etc (quite a contrast to the UK, where teaching is just a voluntary thing to get some extra money in, and adequate funding can be attained without any teachin whatsoever). The latter years of the PhD, most students are supported by research assistantships (RAs).
From what I've read, it seems that funding is just as readily available for international students as it is for domestic grad students. I've not heard anyone say that they believe it to be more competitive for internationals, I hope not anyway. (well I heard it was tricky to get into some of the UC's as an international student, but I don't know if this is true or not).
Like ScotchDave said, you will need to take the General GRE as well as the Subject GRE. My advice to you would be to take the Subject GRE after your second undergrad year, assuming the maths subject test is similar to the physics GRE, you will have covered all the content by this time, and it will be very fresh in your mind. Saves a lot of hassle going back to try and revise later on (even if the content is basic, it's just a pain).