I have an '08 Mac Pro. If I try plugging in my Belkin N150, it works. Then if I plug in my iPad to the slot beneath it, the wireless kicks out. Then if I plug the wireless back in, they both work. So I think the slots are competing for power? What are some solutions?
The iPad is a high power draw device, and Belkin N150 USB Wireless adapter probably is no power slouch either, so it is technically possible for them to be overdrawing an internal USB Bus or Hub in the Mac Pro.
The Mac Pro has 5 independent USB Buses as noted in the picture below.
Now depending where things are plugged in they show up in different USB Buses, you may want to Open your System Information Application, and try to avoid placing the iPad and the Belkin N150 on the same bus.
For Example, on my computer the ZyXel... and the DataTraveler are plugged into front USB ports and they appear to be sharing the same usb tree. While my external Hub labeled "Generic USB Hub" and my VF0680, CIRCA102 are all plugged in rear usb ports on the Mac Pro, note how the CRCA102 is on its own Bus.
Could you not connect the Belkin router via Ethernet rather than USB?
You may want to ensure that you computer isn't trying to use the iPad as a modem when it's plugged in: System Preferences > Network.
By the way you can find out how much current each USB device is drawing in System Information/System Profiler under Hardware > USB.
Usually if devices are drawing too much power, you'll receive an warning message such as this: http://i45.tinypic.com/accqok.png.
Here is an an Apple support document which could explain more: http://support.apple.com/kb/HT4049. It looks as though, unless you receive that message, other USB ports shouldn't be affected by requests for "additional" power by your iPad.