TrueMobile 1150 and switching Access Points

I have a Dell Latitude C640 with a Truemobile 1150 802.11b mini-PCI
card. I run Win2k SP4. I have 3 access points (Siemens Powerline
802.11b transmitters)in my house, all on different channels, each at
least 5 channels away from its neighbor. My router is an SMC Wireless
Barricade. No WEP. All Access Points have the same SSID.

The wireless set up works flawlessly except for one problem. When I
move the laptop around the house, the internet connection dies for
about 5 minutes if I go from one access point to another. The signal
to the new access point is picked up by the Truemobile card instantly
and fully, but no surfing allowed. After about 5 minutes, the
internet connection spontaneously reappears. It is driving me nuts.
I know the answer must be easy, but it is obviously outside my
knowledge base. Any help is appreciated.