Reboot needed to access wireless

For about the past week I've been having problems connecting with my Macbook to my home wi-fi and the wi-fi at my girlfriend's place.

Though Airport will show it's connected automatically, there's no connection to the Internet. I've tried renewing the DHCP Lease, deleting the connection and letting it re-establish, assigning other DNS servers and none of those work. The only way I can get connected is to turn off Airport, delete the network I'm trying to connect to, reboot the Macbook, then turn Airport back on. It then will immediately connect to the network.

But, the next time I boot up the laptop I again can't connect.

Help, please.

Reboot needed....

I am experiencing a similar problem. On my Macbook Pro and even on my older iMac, I will show all the "bars" of the wireless network in my home. I can access, and continue to receive mail in the Mail program, however, if I try to get on the internet, I get timed out that it can't access the server - that it may be busy, etc. Most of the time I have to reboot the computer several times in order for it to come back to the internet. I have a "clue" as to when this is going to happen because the updated checkmark on my tiny little dropbox icon in the top bar of my computer suddenly disappears when I am no longer able to connect to the internet. Sometimes it goes out and then a bit later will come back. It was suggested that I specify the IP address as opposed to letting it randomly select the IP address between a range of numbers, but oddly on my older Macbook Pro, this has never been an issue. On the two PCs in the house, there is no problem with the connection. It seems to be a Mac issue alone and is getting very annoying to have to save work, restart the computer, see if there is a connection, and then often, do it again. Perhaps the same fix could work for both problems? Any suggestions would be greatly appreciated!