Ok, southbridge issues usually start showing other problems then USB. alright so if it's not a driver issue then you would need to reflow/reball the SB. That is very difficult to do and requires special equipment and experience. You could have a shop do it for you and it should not be all that expensive, esp if you find the chip you need and ship just the MB in to them. + more to it then that, confirming the problem on their end too...........
Like i mentioned in my other answer, and someone else did too, a short or even long term solution would be to get a USB PCMCIA card.
I don't like the idea of having some kind of adapter card hanging out of my laptop any more then anyone else I would guess, brings me back to the late 90's.
To sum up, the laptop is fairly old, and the repair isn't expensive but not cheap either when considering the value of the laptop (approx cost of the repair ), + finding a shop that will do it and do it cheap and right.........so a temporary work around might be the best approach due to the value of the machine and the cost of the repair.
You could also replace the motherboard with a used one, that would be cheapest as far as getting it fixed, but that is also a considerable amount of work and calling microsoft about license etc etc......but could be done yourself.
I don't wish to diminish the want or need to self repair but as far as this specific repair, actual repair of the part etc......... not possible even for the older repair guys i know with 30yrs soldering experience without giving them the proper expensive equipment........OR unless you have A-team music and an arc welder then your set.....
replace the MB or sell for parts and buy a T61 for $250