I think Radio shack remote controlled cars, trucks and boats are awesome. They are well made and can last a lifetime if taken car of.
My grandfather gave me a Electric Tandy remote controlled boat when I was a kid. I think I was about 12 years old.
We would visit a few times a year and my grandfaher kept the boat there so I could run it on the the lake behind his house. I think if he would have let me take it home at that age I would have destroyed it.
Well he gave it to me a few years ago, which I had forgotten about it and had not seen it for quite a few years.

I have it at home now, seventeen years later it still runs as if it was brand new. The plastic has turned colors slightly but still runs great.

I can still remember the first day I put that boat on the lake, From that day forth I have always been intriqued by anything remote controlled.

That said I wouldnt suggest a radioshack car as a hobby grade car, thats not really the point of the radio shack line. But certainly great for younger kids and for anyone really that does not want to get serious and spend money in this hobby.

As for the tires I can tell you that you are going to have to fabricate something. I have a Radiosahck ford f150 and had the same problems that you are having with the tires.
Like dirtman said you can get some HPI rims or any 2.2 size and create something that will bind them to the axles. Once you do that you can put any tires you want on there.
If you cant seem to figure out a way to do it, find someone you know that is good at building stuff and so forth. They should be able to put something together fairly quickly.

As well you might post some pics up here on the forum of the truck and close ups of the axles where they meet the wheels.
Maybe some of us can help you come up with something.

Dbow