Whenever I try to change my mac address, I can no longer connect to any network, even networks that I have never connected to before. I am running Ubuntu 9.10 on my Dell Inspiron B130 laptop.

I've tried changing the MAC with macchanger and just by typing in the command line
sudo ifconfig eth1 down
sudo ifconfig eth1 hw ether xx:xx:xx:xx:xx:xx
sudo ifconfig eth1 up

After I change the MAC I run ifconfig and it shows the new address correctly, but when I try to connect to a network, it gets hung and never connects.

If I change my MAC back to its original value then it works just fine.

Any ideas?

What if you restart the NetworkManager?   I could also be a driver issue.  Anything in the dmesg output that's out of whack after you change your MAC?  (that rhymes). 

I'm sure that my wireless card is eth1, and iwconfig confirms that.

I've also tried to restart my network manager by typing sudo /etc/init.d/networking restart, but that doesnt seem to work.

I think that it might be a driver issue. I can't get wireshark to work either, even if I put my NIC in promiscuous mode. I have a Intel PRO/Wireless 2200BG Network card, and I think my driver is ipw2200.      lsmod | grep ipw says

 libipw                 43148  1 ipw2200
lib80211                6432  2 ipw2200,libipw

as for dmesg. I'm a linux newbie and I dont understand how to use that command. =(

I appreciate your help though.

In Ubuntu, you may also need to restart network-manager:

/etc/init.d/network-manager restart

Good luck!

Actually, while not having given you the 'exact' command-line syntax, that's what Ketchup had told you to do, previously.