Are the packages from apt.wxwidgtes.org visible in your package-manager ?
If not, did you update the lists after adding apt.wxwidgets.org ?
I just tested it on ubuntu 10.04 (under qemu-kvm) and it works as expected.
Did you import the wxwidgets key as described on my site ?
Normally it should warn about untrusted key, but work anyway,
nevertheless it might be wort a try:
wget -q http://apt.wxwidgets.org/key.asc -O- | sudo apt-key add -