Same problem here.
Galaxy Tab, Froyo, Vodafone firmware P1000BUJI5.
I was connecting to my neighbor's WIFI router (he gave me the WPA password), and the first day I connected without problem.
Since then I cannot anymore connect, it always get stuck at the "Obtaining IP Adress" loop. At the same time I still can connect without problems with my laptop (ubuntu) and Nokia E71 mobile phone.
It's a brand new Galaxy Tab and I'm thinking to return it if the problem persists.