I have several t40 laptops(similar to yours); forget about using the internal wifi card, it is on the same level as those inferior brands I mentioned.
I use the 2.0 usb ports with the alfa usb 500mw adapter or other adapters using the realtek chip. The acquiring address problem I had with linksys and netgear products; due to the weak signal strength + inferior drivers+ crappy hardware with a built in "antenna"??= crappy performance/ invalid ip 169.xxx,
all types of problems. I have been experimenting with wifi products for at least 5 yrs. I am very familiar with this problem and am by the way a laptop tech as well(working with computers and OS since 2000).
If you don't want to take a chance on something new or don't have the bucks, that's on you. But as Obama said;"if something doesn't work(Middlle East situation) you have to try something else."
The ball is in your court, you can continue to deal with an annoying situation as you are doing or try new products as I have suggested.
If you don't want to invest in quality wifi hardware, you will continue to suffer with the symptoms.
And that goes for everyone else on here who is dealing with the 'acquiring ip address' problem.
End of post.