I am also having problems with IPTables myself...
The weird thing is I get different problems everytime I compile the kernel
There is one odd one which I encountered recently, the IPTables work fine in kernel 2.6.4, I was so happy since I compiled the filters as modules...
But when I went back to my old (original) kernel, I get IPTable failures! haha
Andrew: I agree with your method since I got it to work last time