Overlanding Africa - travel partners?

Hi guys. U may see this post popping up in a few places just because im trying to get answers/opinions from as many people.
I am 27 and will be travelling more than likely on my own. Im goin to be travelling from next year – aug/sept 2012 – long time away but need to get planned. Ive got a good job and prospects but don’t want my life planned out for me now! Could be in that same job for the next 30 years and it scares me to death! Travelling gives me a break and an excuse to get off the hamster wheel!
Im thinking of going overlanding in Africa and maybe in South America. Anybody any info on these? Eg group dynamics, company to go with. Is it just luck? Mainly due to the fact I am travelling alone and would rather have the same people to travel with rather than changing day/week by week.
Im also thinking of doing some volunteering in Africa, maybe Tanzania and also south America. Not sure whether to have set dates for these or find a place when im there. This would mean having open dates for being in Africa and South America and travelling from place to place.  This concerns me that I may spend a lot of my time when travelling making decisions!
Also I do want to go to South East Asia including Malaysia and Indonesia to do Jungle Treks!
Any advice on any of these such as planning, way to do it or what to join me!! Please get in touch any info would be greatly appreciated!!
Bye for now
Claire.

I have done Oasis Overland in the Middle East and it was great and theor Africa trips come reccomended, I also hear very good things about Absolute Africa

Dragoman is also well recomended but can be more expensive which can result in higher chances of older average age

Where abouts in Africa are you looking to go?
I’m starting in Sept/Oct 2012 and going from Kenya to South Africa (inc. Uganda, Tanzania, Malawi, Zambia, Zimbabwe) if you would be interested in that sort of route?