VB,
Would have posted plenty of thoughts and tips earlier but currently been in Vietnam for a few weeks and out of internet range. I can only offer advise for SE Asia....
Agree with all the points made, not much more for me to add. I spent a few years with a backpack birding round SE Asia for 7 months at a time, can't recommend it enough. First things first, get yourself Lonely Planet guides, invaluable for finding cheap digs and locating bus stations, routes and offers insights to the countries history etc. You can buy these as you go along, all backpacker areas in each country sell the neighbouring countries guides, to save space.
Costs - On your own expect to live on 20-30USD a day, Asia countries are steadily increasing in price, cheap accommodation. When you can, team up with others, sharing costs (taxis to airports, bus stations etc) this may only save 50p a time but it soon adds up and can reduce costs to under 20USD a day. Alot over 7 months.
7 months in SE Asia can get you to many countries. If your starting in April, spend a month in Thailand or Vietnam, moving south to Malaysia for May (I have an apartment here, no probs staying with us on the couch, saves you some pennies and we can give you some local info), June visit Sabah, Borneo, an absolute must, spend at least a month here (Danum Valley Field Centre will cost 30USD a day). July and August could send you to Indonesia (ignore anyone who tells you its dangerous blah blah, it is is b*&^%$), start in Sumatra and work your way eastwards through Java then spend a week or so relaxing in Bali and visit Komodo Island and Flores, wonderful islands. From September weather isn't so good in SE Asia, so if you want, carry in to Oz, easy to do from Bali, or fly back to Singapore and fly Tiger Airways to Darwin.
Alternatively, look at visiting Sichuan, China in May/June, Vietnam in March (a budget country that is superbly setup for backpackers and birders). Birding in Cambodia is out of budget for single birders unfortuntely.
Hope this helps a little, e-mail me if you need more advise.
James