Courts have used the following criteria re trademark analysis:
1) Are the goods/services sold in the same marketing channels?
2) Do they compete?
3) How similar are the marks in sound appearance and meaning?
4) How strong is each mark (distinctive?)
5) How much time does a consumer spend looking into the purchase/how much does it cost?
6) Are the marks used on several differnet goods/services?
7) Do the two marks share the same customer base?
The first three are the most important. If the first three don't lead you to a "Yes, its ok to use this mark" answer, you have a close case. If the next four don't fall in your favor, then its best not to even try. Once your business becomes profitable, the trademark owner will seek to take your profits in court.
Trademarks operate on a spectrum of interpretation by courts. The more arguments you have in your favor the safer you are. Thus, to be extra safe in protecting your business name, use a commonly used type name describing the product/service or a very distinctive name apart from all others. All cases in between can be subject to dispute to some degree or another albeit with very different outcomes. Its about managing your risk and you get to decide how risky you want to be in choosing your name and if its similar to another profitable company's name, you may get away with it for awhile, but once they notice your stealing business, rest assured they will want to take it back any way they can. I hope this helps and I would appreciate any accept you provide.