Have a male friend who is Australian,he is in Malaysia trying to get back to Australia, went to check in at airport and they told him he didn't have enough BTA ,is this fact true ?
And how much dose he need.

This is a SCAM. This is one of the Nigerian scam...

Do not send money, tell him to contact the Australian Embassy in Malaysia for help.

Check full header of emails he sent you, you will find those were send from IP address in some country in Africa.

He has contacted them at the Australian embassy in malaysia they have given him a ticket but when he went to check in at the airport they told him he needed $600 BTA,he hasn't got it, he went back to the embassy but they said they couldn't give him any more.

He has been talking to me for 2 years now through Yahoo I'm ,not through emails.

The term "allowance" is a clue that this is wrong. How can an "allowance" be required, unless its given by the Malaysian government? scam.