I have this problem also, my setup is as follows....

HP C5180 Printer connected to DLink DSL-G604T Wireless modem router
via Cat 5 cable. Vista Home Basic Laptop (Dell Inspiron 6400)
connected via Wireless.

Every couple of days the Printer Driver for the C5180 completely
dissappears from the laptop machine and needs to be re-installed.
Once the driver/software for the printer is re-installed everything
works fine for another couple of days, and then the same thing occurs.

I am continuing to troubleshoot this problem (much to the displeasure
of my client), but hope to find a solution soon, else something will
be thrown out the window.