Hi, Neil. There was an article in the Detroit News a few months back about a company that was ripping people off. If you search the board, you should be able to find the link. At the same time, there are many good window companies out there and I certainly don't want to tar them all with the same brush.
Those 2 companies have been around for some time, which is a good sign. But you should still check with the Better Business Bureau and ask the companies for references from other customers in your local area. On our street of 30 year old homes, probably half of them have new windows. They should have lists of satisfied customers close to you. Then call or visit your neighbors and ask them.