That website should tell you all you need to know.
You need to be above 47kg (not a problem for most of us I'd say!) and below about 160kg (I think that's because of the chairs..), in reasonable health, with no blood borne diseases (HIV positive need not apply..).
Any questions, call 13 14 95 and they can give you more information.
In general - drink LOADS of water on the day (at least 2L) and make sure you eat reasonably well before you go!
Passing out/feeling sick is relatively common. I usually feel like I'm going to pass out, and have actually fainted a couple of times. I don't know why I go back, masochistic I guess!
What you can do:
--DISTRACT YOURSELF (bring a friend to chat to/hold your hand, watch the TV, read a magazine, just don't look at the blood coming out!)
If you've fainted before, learn to recognise the early warning signs and TELL THE NURSE! Right away, don't be embarrassed, it's very common! For me, I start feeling hot and sweaty and I know I'm going to faint very soon!
Afterwards - you lay down in the chair for a while and sit and drink juice until you are feeling completely fine, then you eat your complimentary snacks and DRINK MORE WATER!
If you're worried about fainting etc, bring someone to drive you home.
In general - it's a fantastic thing to do. It can help SO many people out there in need, and blood stocks in Australia are really low at the moment so NOW is the time to give! There are benefits to you too - you feel fantastic, rack up the good karma points, burn calories (as your metabolism kicks into overdrive to replace your red blood cells) and get lots of compliments when people realise you just donated blood!
So check out the website above, and call 13 14 95 for an appointment!