Bit late but... the poster above was suggesting to try using the power line method to get from house to garage. It is possible to send an IP signal through your house electrical wiring. He suggests putting an adapter in the house and one in garage. Then in the garage put the wireless transmitter and broadcast there.
However, that would require the electric cabling for the garage to be on the same circuit as the house, which may or not be the case.
Google for "netgear powerline adapter" to find out more. Useful in many circumstances.
The issue you are having though, is your garage materials. Metal does block wireless, so either bigger ariels, or directional ariel. However the CAT5 is going to be best overall
Thanks @Peter. What you state is what I had believed the other member was saying. In Canada we seldom refer to A/C as 'Mains' but I know in Britain it is the common terms, even in labeling of electrical devices. My own investigation turned up the same proviso, must be a common circuit (in Canada, 'branch'). My problem with this is that we have one meter, and both 'mains' branch from that, so there is nothing in common without passing through the meter, itself. Mains idea shot to hell.
There is a caveat though in using these powerline Adaptors. Most domestic circuits are divided into different groups based on the usage. Circuits which feed appliances may contain power factor correction capacitors which will attenuate your RF signal. Extension adapters designed for sensitive computer equipment will contain toroid wound filters/capacitors specifically designed to attenuate RF. So at the end of the day, you may or may not get decent connectivity depending on the overall attenuation along the power line. There is still nothing to beat that CAT5.
I'd say this question is resolved, in that I have lots to explore, and good information to continue with. Thanks, everyone. I'm off to dig a trench in the snow, drill a hole in some walls, mount a shelf for the router, and put this project to bed. CAT5 it is.
... and throw some wood on the fire. It must be cold out there?