Im coming up to my viva and wondered if anyone who has had theirs could tell me whether I should be spending time reading up on my examiners papers (his topic is not very closely related to mine) or not and whether he is likely to discuss general things about the wider area of (in my case ecology) or if they stick largely to the phd topic and the thesis in particular? My supervisor has been really unhelpful with advice and Im getting really het up about it.

Anyone got any general tips? Is it really like a 'defence' ie should I be on guard the whole time or is it more of a discussion? can I agree with the examiners criticisms? will he expect me to tell him the criticisms i have of my own work? or will this make me look incompetent...
help!
Also was anyone told they had passed before the viva started?

See http://www.geocities.com/andrewbroad/cs/cs710/viva.html
It explains the types of questions you will be asked.
I would find out what your examiner does, they may have an interest that overlaps. If they know about an area they are more likely to ask you about it.
The discussion depends on what you have written, you are expected to have some general knowledge. It tend to be based around the thesis. Perhaps you need someone to predict some questions for you to give you
Mine was a series of questions. I found a lot of criticisms with my work before submission and picked a nice examiner as I'm not so confident and it went very smoothly. They are not trying to trip you up, some questions will be because they are interested or just don't know that area well.
Also was anyone told they had passed before the viva started?
No, you leave for 5 mins while the examiners discuss then come back. You can gauge by the questions e.g. minor points or gaping holes in your thesis.

the viva is a defence but not in the context of facing an attack - or at least it shouldn't be! Its in the context of justifying your research decisions. If you know why you did everything you did and can confidently support your findings you should be ok - this is the kind of defence you need to put forward. If your externals work is not very similar to your own, you can not be expected to be very familiar with it - it would be courteous to be able to talk about it at some level. If it is related to your research, know it in that context.Good luck, its more frightening before than during!

I tried to read a lot of my examiner's papers before my viva, and it wasn't worth it. He did mention 'we do xxx' at some point when it had a slight connection to my work but I just had to nod and smile which frankly I could have done without reading the relevant papers!!
My viva was very specific to my thesis - page by page really. 'I had a query about something on page x', then we all turned to that page and I had to make some sensible comments. The examiners reassured me before the viva started that the purpose was for me to prove to them that I, and not someone else, wrote the thesis.
They asked me lots of questions that I had anticipated, but I was in a bit of a state beforehand so hadn't really spent a lot of time actually trying to find the answers - that was a bit irritating. Well, that's not entirely true. They were questions that I had made attempts to answer during the four years of my PhD but hadn't been able to, so in that respect the viva was quite difficult.

Overall, I don't think my viva went well, I didn't 'perform' well at all, but I was so worn out by the end my mentality was just to get it over with. I didn't go out on a high, but I think that's okay - I get the impression that everything doesn't rest on your viva performance.

Oh, I forgot to say - I passed with minor corrections.

"My viva was very specific to my thesis - page by page really. 'I had a query about something on page x', then we all turned to that page and I had to make some sensible comments."
That was how my viva went too

My viva was similar to those already descirbed, very specific to my thesis. This was the external's first PhD viva and he seemed to get a bit carried away, it lasted 4 hours, after 3 of which we were only half way through the thesis! In general, questions were straight forward and the examiners offered a lot of useful explanation and advice on areas they felt where the thesis was weak. I genuinely learnt alot from this experience. Passed with minor corrections, into the home straight !

thanks for all that advice people, is very reassuring and feel better about facing it now...

Don't try and second guess it - my supervisor told me this along with ' once you have had a viva, you will never be the same again'... I still wonder if mine was real as it was so different to all the stories I heard...

I'd say get a good nights sleep and make sure you're confident on what your main contributions were.. anything else is up to your examiners...

Oh.. and be polite 'Whilst I can see your point, what I meant was...' and 'Yes, I can see why you might look at it that way, however I feel....'

As long as you can 'prove' your points.. I bet you'll be fine :)