I've seen all sorts of weirdness during my wireless installs,
you could try a few things...
Simplest is to try another card on the Compaq's, I've had specific issues with different vendors cards not working right with certain brands of notebook.
What brand/chipset access point are you using?
What brand/chipset wireless card is it?

Most proxim/agere/ lucent based cards are 5V I've had issues where the notebooks PC Card slot is only supplying 3.3V or cannot supply 5V properly.
You could switch the pc card slot on the notebook from, "Auto / 16bit compatible / Cardbus....

You could set the "Preamble" from short to long or vice versa on the access point to see if it makes a difference.
Interference Robustness or similar setting.
Change Channels.
Turn off WEP or any security if it's on to test.
Turn off any vendor specific settings on the access point, i.e. Speed Boost etc..

You can try AdHoc mode between both the cards in the Compaq's and see how far you get by emliminating the access point.